The two triangles are similar. The two marked sides 16 and 2x-6 are connected in such a way that the longer side (16) is exactly twice as long as the shorter side (2x-6)
In other words longer side = 2*(shorter side) 16 = 2*(2x-6)
Let's solve for x 16 = 2*(2x-6) 16 = 2*2x+2(-6) 16 = 4x - 12 4x - 12 = 16 4x - 12+12 = 16+12 4x = 28 4x/4 = 28/4 x = 7 which is the answer
