Joining midpoints(a line segment MN is formed) tells you that you have a line MN that is 1/2 the length of GH
MN = 1/2 GH
MN = 1/2 (8x + 2)
13 = 1/2 (8x + 2) Multiply both sides by 2
13 * 2 = 8x + 2
26 = 8x + 2 subtract 2 from both sides.
26 - 2 = 8x
24 = 8x Divide by 8
24/8 = x
x = 3