Balloon Cart with Proportional Deceleration

1#include <AFMotor.h>    //Adds Motor shield library
2
3#define trigPin  7
4#define echoPin 6  
5
6float v;
7int duration;
8long distance;
9long  distance1;
10long distance2;
11
12AF_DCMotor motor(1);
13
14void setup() {
15  Serial.begin(9600);
16  pinMode(trigPin, OUTPUT);
17  pinMode(echoPin, INPUT);
18
19  motor.setSpeed(200);
20  motor.run(RELEASE);
21}
22
23void loop() {
24  do{
25  distance = (duration/2) /29.1; 
26  digitalWrite(trigPin, HIGH);
27  delayMicroseconds(1000);
28  digitalWrite(trigPin, LOW);
29  duration = pulseIn(echoPin, HIGH);
30  distance  = (duration/2) /29.1;
31  Serial.print("distance ");
32  Serial.print(distance);
33  Serial.println("cm");
34  }while(distance <= 4 || distance > 40);
35
36 do{
37  digitalWrite(trigPin, HIGH);
38  delayMicroseconds(1000);
39  digitalWrite(trigPin,  LOW);
40  duration = pulseIn(echoPin, HIGH);
41  distance1 = (duration/2) /29.1;
42  Serial.print("distance1 loop ");
43  Serial.print(distance1);
44  Serial.println("cm");
45  delay(100);
46  v = ((float)distance1/(distance+1))*255;
47  Serial.print("speed  ");
48  Serial.println(v);
49  motor.run(FORWARD); 
50  motor.setSpeed(v);
51  Serial.println("Forward");
52 }while(distance1 > 5);
53
54motor.run(RELEASE);
55motor.setSpeed(0);
56delay(3000);
57
58do{
59  digitalWrite(trigPin, HIGH);
60  delayMicroseconds(1000);
61  digitalWrite(trigPin,  LOW);
62  duration = pulseIn(echoPin, HIGH);
63  distance2 = (duration/2) /29.1;
64  Serial.print("distance2 loop 2 ");
65  Serial.print(distance2);
66  Serial.println("cm");
67  Serial.println("Backward");
68  motor.run(BACKWARD);
69  motor.setSpeed(150);
70}while(distance2  <= 19);
71motor.run(RELEASE);
72delay(3000);
73}