16.9115345253. Espero que esto ayude!
X = cost of 1 sweat shirt
3x = 45
x = 15
5x = 5(15) = 75
It would cost $75. Hope this helps!
Total Cost in a day is

. Profit function is

. And the revenue function is

. In a day, bookstore must sell at least 15 books, because of 6n-90=0, in order to make profit.