Find the limit as x approaches 4 of the function f(x) defined piecewise as follows:
f(x) =
2x if x is less than 4
15 if x is equal to 4
56 - 12x if x is greater than 4
Which of the following correctly represents the limit as x approaches 4 of f(x)?

a) 8
b) 15
c) 32
d) 68