Answer:
Because you know two sides of each triangle and they are the same triangle just the small triangle is a ratio smaller put the sides into a fraction and set them equal
Explanation:
15 / 4x = 12 / 3x+1 then cross multiply
15(3x+1) = 12 ( 4x)
45x+15 = 48x
15 = 3x
5 = x
this is a tricky problem