Your making big several purchases from the b better electronic store. you can buy from this store online or in a physical store. you have a coupon for 20% off that can only be used in the physical store and a 20.00 coupon that can only be used online. the sales tax of 7.5% only applies to the physical store. shipping for the online store is a flat rate of 8.99 or free for purchases over 75.00. which way of purchasing would save you the most money?

I can write give you an answer with an assumption. Say you want to buy $500 worth of products. If you go to the store, you get 20% off, but you pay 7.5% tax on it so:
$500-20%=$400
That's $100 off makes sense because $100-$20= $80x5=$400
you don't get 20% off sales tax, so we do 
$400+7.5%=$430
That's $30 in taxes.

If you would do it online, it would be:
$500-$20 online coupon is = $480
shipping is free because I'm over $75

So which one is less? The in-store purchase because it's $430 vs online is $480. Online is $50 more than in-store. 

Graph a should be your answer