Final version of the code:

// —————————————————————————
// Example NewPing library sketch that does a ping about 20 times per second.
// —————————————————————————
#include <Servo.h>
#include <NewPing.h>

NewPing sonar1(12, 10, 200); // Sensor 1: trigger pin, echo pin, maximum distance in cm
//NewPing sonar2(7, 6, 200); // Sensor 2: same stuff

const int numReadings = 18;
int fr_readings[numReadings];      // the readings from the analog input
int fr_index = 0;                  // the index of the current reading
int fr_total = 0;                  // the running total
int fr_average = 0;                // the average
// initialize buffer

int bk_readings[numReadings];      // the readings from the analog input
int bk_index = 0;                  // the index of the current reading
int bk_total = 0;                  // the running total
int bk_average = 0;                // the average

int sm_average = 0;

#define pingSpeed 100 // Ping frequency (in milliseconds), fastest we should ping is about 35ms per sensor

Servo LeftServo;
Servo RightServo;

int val_x; //front proximity sensor
int val_y; //rear proximity sensor

//NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.

void setup() {
  LeftServo.attach(13);
  RightServo.attach(4);
  //Serial.begin(9600); // Open serial monitor at 115200 baud to see ping results.
    // initialize all the readings to 0:
 for (int thisReading = 0; thisReading < numReadings; thisReading++)
    fr_readings[thisReading] = 0; 
     //for (int thisReading = 0; thisReading < numReadings; thisReading++)
   // bk_readings[thisReading] = 0; 
     RightServo.write(0);
 LeftServo.write(0);
 //delay(2000);
}

//void compareDistance() {
//   Serial.println(fr_average);
//   Serial.println(bk_average);
//     Serial.print(“sm_average: “);
//   Serial.println(sm_average);
//  if (fr_average < bk_average) { //if someone is closer in the front
//     sm_average = fr_average;
//   }
//   else {
//     sm_average = bk_average;
//  
//   }
// }
  

void loop() {
  delay(50);                      // Wait 50ms between pings (about 20 pings/sec). 29ms should be the shortest delay between pings.
  unsigned int uS_front = sonar1.ping(); // Send ping, get ping time in microseconds (uS).
 // unsigned int uS_back = sonar2.ping(); // Send ping, get ping time in microseconds (uS).
  //Serial.print(“Ping: “);
 // Serial.print(uS / US_ROUNDTRIP_CM); // Convert ping time to distance in cm and print result (0 = outside set distance range)
  //Serial.println(“cm”);

 val_x = (uS_front / US_ROUNDTRIP_CM) ;
  Serial.print(“val_x2: “);
 Serial.println(val_x);
  val_x = map(val_x, 8 , 130, 0, 90);
 val_x = abs(val_x);

//  val_y = (uS_back / US_ROUNDTRIP_CM) ;
//  val_y = map(val_y, 0, 200, 0, 90);
 
 //Serial.print(“val_y: “);
  //Serial.println(val_y);
   // subtract the last reading:
   //if (val_x
  fr_total= fr_total – fr_readings[fr_index];   
  //bk_total= bk_total – bk_readings[bk_index];  
  // read from the sensor: 
  fr_readings[fr_index] = val_x;
  //bk_readings[bk_index] = val_y;
  // add the reading to the total:
  fr_total= fr_total + fr_readings[fr_index];    
 // bk_total= bk_total + bk_readings[bk_index];     
  // advance to the next position in the array: 
  fr_index = fr_index + 1;    
 // bk_index = bk_index + 1;    

  // if we’re at the end of the array…
  if (fr_index >= numReadings)             
    // …wrap around to the beginning:
    fr_index = 0; 
 // if (bk_index >= numReadings)             
    // …wrap around to the beginning: 
   // bk_index = 0;      

  // calculate the average:
  fr_average = fr_total / numReadings; 
 fr_average = abs(90-fr_average);
  //bk_average = bk_total / numReadings;   
  // send it to the computer as ASCII digits
 //  Serial.print(“average: “);
 //Serial.println(fr_average);
// compareDistance();
 //  sm_average = fr_average;
 RightServo.write(fr_average);
 LeftServo.write(fr_average);
//  Serial.print(“Front average: “);
// Serial.println(fr_average); // Convert ping time to distance in cm and print result (0 = outside set distance range)
//Serial.print(“Back average: “);
//Serial.println(bk_average);
 delay(50);
}