Answer:
When the price of the stereo is more than $80, then it will be cheaper to buy the stereo online.
Explanation:
Lets us assume that the price of the stereo is x.
If Jay buys online he gets a 15% discount, but has to pay a $12 shipping fee.

=>

So, x = 80
And 15% of 80 is :
dollars
Jay saves $12 but he has to spend $12 in shipping.
Up to $80, it does matter whether Jay buys the stereo online or at the store.
But when the price of the stereo is more than $80, then it will be cheaper to buy the stereo online.