Step-by-step explanation:
the small and the large triangles are similar triangles.
they have the same angles. and the corresponding sides correlate to each other with the same ratio for every pair of sides.
so,
28 / 82 = (2x + 8) / ((2x + 8) + (5x -4)) =
= (2x + 8) / (7x + 4)
(7x + 4)×28 = (2x + 8)×82
196x + 112 = 164x + 656
32x = 544
x = 17
