A certain company sells sweatshirts for $$20$ if you buy $10$ or less. If you are willing to buy between $11$ and $50,$ they will cut a deal and sell then for $$18$ a piece. Additionally, if you are willing to buy more than $50,$ they will sell them for $$16$ apiece.

$3$a$.$ Create a formula for finding how much it will cost the customer f$($x$),$ based on the appropriate selling price and the number of shirts $($x$-$value$)$ bought

$3$b$.$ What can you say about the behavior of this graph and the relationship between the cost of the shirt and the number of shirts?

$3$c$.$ How much would a person spend for buying $35$ shirts? When do you think this pricing is not cost $–$effective with the consumer and the seller?