Well, the equation for this problem is 5.50x + 8.00.
The y-intercept / initial value in the problem is $5.50 because that is what you have to pay and it’s basically your initial value whereas $8.00 is your slope or rate if change because that is why you have $8.00x which means that whatever number of sweatshirts you buy, they will each cost you $8.00.