Write three functions (1) rectangleArea (2) circleArea, and (3) triangleArea to compute and return?

... the area of a rectangle, circle, and triangle, respectively.
Use these functions in a program in which program will compute and print the area of
(a) rectangle if user will enter ‘R’ or ‘r’;
(b) circle if user will enter ‘C’ or ‘c’;
(c) triangle if user will enter ‘T’ or ‘t’;
The program will discontinue (stop) if user will enter ‘E’ or ‘e’