What could be a prototype for a C++ user-defined function say mean...), which receives three integer numbers and returns their average value? Select one O a float mean(void, vold, void) O b. float mean(int, int, int): O c void mean(int, int, int): od mean(int int, int); Oeint mean(int int int); What will be the output: Consider the following code: int x= 3.n; n = 2/2"X++ cout