In problem A, it looks like they are trying to get you to find the break-even point per unit... Which if we look at A, we get 84$ in costs,with a selling price of 90$.

$18

$6

$36

$9

+$15

$84

Which means that the break-even point would be 6$ (With a price set at 90$)

Which means that if you add up total costs of the other products, and then add 6$ to that, you should have your answers to pricing B and C... But, that's just how the problem reads to me...