What is the next number in the series below?

What is the next number in the series below?

3 16 6 12 12 8
A . 4
B . 15
C . 20
D . 24
E . 32

Answer: D

Explanation:

This series actually has two alternating sets of numbers. The first number is doubled, giving the third number. The second number has 4 subtracted from it, giving it the fourth number.

Therefore, the blank space will be 12 doubled, or 24.