Explanation:
similar triangles mean that all angles are the same, and the side lengths of one triangle correlate to the corresponding sides of the other triangle by the same factor.
that means that the sides 2 (ED) and x (CB) have the same relation as the 6+4 (AD) and the 6 (AB) sides.
so,
x/2 = 6/(6+4) = 6/10 = 3/5
x = 2 × 3/5 = 6/5 = 1.2