Answer:
 x = 17 1/3
Explanation:
Corresponding segments are proportional.
 (3x)/(4x) = (3x +7)/(5x -8)
 3(5x -8) = 4(3x +7) . . . . . . . . multiply by 4(5x-8)
 15x -24 = 12x +28 . . . . . . eliminate parentheses
 3x = 52 . . . . . . . . . . add 24-12x
 x = 17 1/3 . . . . . . . . . divide by 3