C++ please

1. Checkpoint Exercises: Work the following problems in the textbook. Work each problem by hand (not using the compiler). Be sure to write out the instructions for each problem and include the given information. a) (7 pts) Checkpoint Exercise 6.8 on p. 215 b) ( 6 pts) Checkpoint Exercise 6.18 on p. 229 6.8 Write function headers (not the bodies) for the following functions: a. Return a sales commission, given the sales amount and the commission rate. b. Display the calendar for a month, given the month and year. c. Return a square root of a number. d. Test whether a number is even, and return true if it is. e. Display a message a specified number of times. f. Return the monthly payment, given the loan amount, number of years, and annual interest rate. g. Return the corresponding uppercase letter, given a lowercase letter. 5.18 Show the output of the following code: \#include using namespace std; const double PI =3.14159; double getArea(double radius) { return radius * radius * PI; void displayArea(double radius) { cout getArea(radius) end1; \} int main( double r1=1; double r2=10; cout getArea(r1) end1; displayArea (r2); \}