Quiz-5-> Interfacing of Ultrasonic sensor with Node MCU

Q-1-: What is the use of the Ultrasonic Sensor?

Q-2 -:What will happen if we supply a voltage of 25V to the Vcc of the Ultrasonic sensor?

Q-3-: How many pins are present in the Ultrasonic Sensor?

Q-4-: Is the circuit correct? 

Q-5-: What is the final value of the d2 variable?

const int trigPin = 9;
const int echoPin = 10;
long d1;
int d2;
void setup() {
    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);
    Serial.begin(9600); 
}
void loop() {
    digitalWrite(trigPin, LOW);
    delayMicroseconds(2);
    digitalWrite(trigPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(trigPin, LOW);
    d1 = pulseIn(echoPin, HIGH);
    d2 = d1*0.034/2;
    Serial.println(d2);
}