Refer to the Following

Refer to the following:
A news magazine offers students a discount on the regular subscription rate. The total number of subscriptions is optimal, and, at the current prices, the marginal revenue from the last subscription sold to a student is $6, while the marginal revenue from the last subscription sold to a regular customer is $10.
-If the magazine sells one more subscription to a regular customer and one less subscription to a student:

A) profit will increase $4
B) profit will increase $16
C) profit will decrease $6
D) profit will decrease $10
E) none of the above