PLEASE SOMEONE HELP I WILL GIVE BRAINLIEST
(Look at the picture)

The similarity ratio of two similar triangles is equal to the ratio of their corresponding sides :
Similarity ratio = BA / GF = BC / GH = CA / HF
Similarity ratio = 18 / 9 = 14 / 7 = x / 6
x / 6 = 2
multiple sides by 6
6 × x / 6 = 6 × 2
simplification
x = 12