A store owner spends 7x + 13 dollars on two orders of boxes of light bulbs, including shipping.

Part A
If she spends 3x + 5 dollars on the first order of light bulbs, which of the following represents how much she spends on the second order?
A. 10x + 18
B. 4x + 8
C. 21x + 65
D. 10x + 8
Part B
If the store owner spent a total of $90 on both orders, how much does a box of light bulbs cost in dollars?