What is the correct number to fill in the blank?

Answer to the puzzle: 6

Rule: In each row, multiply the difference of the first two numbers (from left to right) by two to get the third number.

We have:

(11 - 2) x 2 = 18.

(5 - 2) x 2) = 6.

(12 - 5) x 2 = 14.