implicit declaration of function "calculation_motor_speed"

This error message means that you are trying to call a function called "calculation_motor_speed" in your code, but the compiler has not seen a declaration or definition of this function before.

To fix this error, you need to either include a header file that declares the function, or provide a function definition before you call it.

Here's an example of how you could declare the function in a header file:

// in motor.h
float calculation_motor_speed(float voltage, float current);

And then include this header file in your main code file:

// in main.c
#include "motor.h"

int main(void) {
  float voltage = 12.0;
  float current = 1.5;
  float speed = calculation_motor_speed(voltage, current);
  // ...
}

Alternatively, you could provide a function definition for "calculation_motor_speed" before you call it:

float calculation_motor_speed(float voltage, float current) {
  // ... implementation goes here ...
}

int main(void) {
  float voltage = 12.0;
  float current = 1.5;
  float speed = calculation_motor_speed(voltage, current);
  // ...
}

Either way, make sure that the function signature (i.e. return type and parameter types) matches the way you are calling the function in your code.