A company charges $7 for a T-shirt and ships any order for $15. A school principal ordered a number of T-shirts for the school store. The total cost of the order was $1,520. Which equation can be used to find the number of shirts ordered A: 1,520 = 7x + 15x
B: 1,520 = x + 15(7)
C: 1,520 = 7x + 15
D: 1,520 = 15x + 7