If a&b = (a - 1)(b - 1), we can come up with an algebraic representation of x&13:
x&13 = (x - 1)(13 -1), or:
(x - 1)(12)
We know that's equal to 96, so we can solve for x:
96 = (x-1)(12)
8 = x - 1
x = 9, choice (C).