Jay can buy a stereo either online or at a local store. if he buys online, he gets 15% discount, but has to pay a $12 shipping fee. at the local store, the stero is not on sale, but thereis no shipping fee. for what regular price is it cheaper for jay to buy the stereo online?

Ok. For any price higher than $80, it will be cheaper for Jay to buy on line. Below $80, it will be cheaper to buy it at the store (assuming that there are no sale taxes)

This is why:

15%/100%= 12/x, x is the price of the car stereo.
(15)(x)=(12)(100)
15x= 1200
x=80 at this price it does matter whether he buys it on line or at the store. Because 15% discount on an item that costs $80 is $12. [ (.15)(80)=12]. He saves 12 dollars but he has to spend 12 dollars in shipping. So, he end up paying $80.. However, if the price of the item is more than 80, it will be cheaper for him to buy on line.