Declare (give a prototype for) a function named average_grade. This function returns a double and has four double arguments, test1, test2, test3, test4. The return value should be the average, or arithmetic mean of the four arguments. Be sure to include a "prototype comment" that tells briefly what the function does.

What will be an ideal response?

//returns arithmetic mean of the arguments test1 - test4
double average_grade (double test1, double test2,
double test3, double test4);