Triangles ABC and ADE are similar (side-angle-side postulate) in a ratio of 2 to 1. This means triangle ABC is 2 times larger than triangle ADE.
This in turn means that BC is twice as long as DE, so
4x - 6 = 2 (x + 1)
Solve for x :
4x - 6 = 2x + 2
4x - 2x = 2 + 6
2x = 8
x = 4