program in C

4. (25 pts) Write a function called to UpperCase that takes a character variable letter as input and returns it into uppercase. If letter is already uppercase or a number from 0 to 9, do not change it. For example, if letter is 'a', return 'A'. If letter is 'A' or 'O', return the same letter. 5. (25 pts) What is the output of the following program? Explain how you get the value. #include int expand(int number, int factor) { return number*factor; int main(void) { int x = 6; printf("%d, %d ", expand(x + 1, 4), expand(expand(x+2, 3), -3)); return 0