Help me, speed with hc-sr04

Projects Programming
3 
distance1 = ultrasonicRead(); //calls ultrasoninicRead() function below
   
   delay(1000);//giving a time gap of 1 sec
   
   distance2 = ultrasonicRead(); //calls ultrasoninicRead() function below
   
   //formula change in distance divided by change in time
   Speed = (distance2 - distance1)/1.0; //as the time gap is 1 sec we divide it by 1.
   
  //Displaying Speed
 Serial.print("velocidad en cm/s  :"); 
 Serial.println(Speed);

I was trying this way but the "ultrasonicRead ()" does not recognize me