Answer:
x = 9
Explanation:
Corresponding sides are proportional when the triangles are similar. That means ...
(x -4)/8 = (x +3.5)/20
5(x -4) = 2(x +3.5) . . . . . multiply by 40
5x -20 = 2x +7 . . . . . . . eliminate parentheses
3x = 27 . . . . . . . . . . . . . add 20-2x
x = 9 . . . . . . . . . . . . . . . divide by 3