a
10.95x + 2.50, but for eight books so 10.95 x 8 + 2.50 = 90.10
b
12.50x + 4.50, but for six books so 12.50 x 6 + 4.50 = 79.50
c
To do this, we can set them both equal to each other and if x is a whole number of books, then they do pay the same amount. If x is a decimal, then they don't pay the same amount.
10.95x + 2.50 = 12.50x + 4.50
2.50 - 4.50 = 12.50x - 10.95x
-2 = 1.55x
This can never be a whole number, so therefore members and non-members can never pay the same amount for an order of x books.
