$($Quality Points for Numeric Grades$)$ Write a function qualityPoints that inputs a student$$s average and returns $4$ if a student$$s average is $90100,3$ if the average is $8089,2$ if the average is $7079,1$ if the average is $6069$ and $0$ if the average is lower than $60.$

$($Reverse Digits$)$ Write a function that takes an integer value and returns the number with its digits reversed. For example, given the number $7631,$ the function should return $1367.$

Write a function that determines whether a number is prime.

$($Greatest Common Divisor$)$ The greatest common divisor $($GCD$)$ of two integers is the largest integer that evenly divides each of the numbers. Write a function gcd that returns the greatest common divisor of two integers.