int DELAY_TIME  = 3000;
int DIGITAL_PIN_8 = 8;
int DIGITAL_PIN_7 = 7;
int DIGITAL_PIN_4 = 4;
void setup() {
  // put your setup code here, to run once:
pinMode(DIGITAL_PIN_8, OUTPUT);
pinMode(DIGITAL_PIN_7, OUTPUT);
pinMode(DIGITAL_PIN_4, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
//RED
digitalWrite(DIGITAL_PIN_8,HIGH);
delay(DELAY_TIME);
digitalWrite(DIGITAL_PIN_8,LOW);

//GREEN
digitalWrite(DIGITAL_PIN_7,HIGH);
delay(DELAY_TIME);
digitalWrite(DIGITAL_PIN_7,LOW);

//YELLOW
digitalWrite(DIGITAL_PIN_4,HIGH);
delay(DELAY_TIME);
digitalWrite(DIGITAL_PIN_4,LOW);
}