The answer is B. C(n) = 0.75n - 0.25.
Let n be the number of pieces. The price for 1 piece is $0.75. The price C for n pieces without a coupon is n * $0.75: C(n) = 0.75n. The coupon value is $0.25. So, this value must be subtracted from the total price of n pieces. Since the coupon values in independent on the number of pieces, the price C for n pieces with the coupon will be: C(n) = 0.75n - 0.25. Therefore, the correct choice is B.