The length of the middle segment is equal to the average sum of the top and bottom segment.
So (3x - 8) + (7x + 4) divided by 2, should be equal to 33.
Work:
(3x - 8) + (7x + 4) = 10x - 4
Divide by 2:
5x - 2
Set equal to 33 and solve:
5x - 2 = 33
5x = 35
x = 7
The answer is E.