Write a simple set of mathmatical functions:

add$(x,y)$Sum of $x$ and $y$

sub$(x,y)$sum of $x$ and $y$

mult $(x,y)$ multiply $x$ and $y$

div$(x,y)>$ divide by $x$ and $y,$ return none if $y=0$

Factorial $(x)x!$

Write a driver program that tests each of these functions