Sol.-

int red=2;
int green=4;
int echo=13;  // echo is used for input
int trig=12;  // trig is used for output
void setup()
{
  pinMode(red,OUTPUT);
  pinMode(green,OUTPUT);
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  Serial.begin(9600);
}
void loop()
{
  int time;
  int distance;
  digitalWrite(trig,1);
  delayMicroseconds(1000);
  digitalWrite(trig,0);
  time=pulseIn(echo,1);
  distance=(time*0.034/2) ; //0.034 speed of sensor 
  Serial.print("Distance in cm is");
  Serial.println(distance);
  if(distance <10)
  {
    digitalWrite(red,1);
    delay(100);
    digitalWrite(red,0);
    delay(100);
    digitalWrite(green,1);
    delay(100);
    digitalWrite(green,0);
    delay(100);
    
  }
  else if(distance<20)
  {
    digitalWrite(green,1);
    delay(950);
    digitalWrite(green,0);
    delay(950);
    digitalWrite(red,1);
    delay(950);
    digitalWrite(red,0);
    delay(950);
    
  }
  else if(distance<30)
  {
    digitalWrite(red,1);
    delay(1000);
    digitalWrite(red,0);
    delay(1000);
  }
  else
  {
    digitalWrite(red,0);
    digitalWrite(green,0);
  }
  
}