Explanation:
similar means they have the same angles, and there is one common scaling factor for all pairs of corresponding sides. we need to find it for one pair, and we then have it also for the x pair and can calculate x.
comparing the sides in relation to each other we find that F corresponds to L, H to J and G to K.
so, the scaling factor of LK/FG is then also the scaling factor of JK/HG.
LK × f = FG
45 × f = 27
f = 27/45 = 3/5
JK × 3/5 = 3x + 6
65 × 3/5 = 3x + 6
13 × 3 = 3x + 6
39 = 3x + 6
33 = 3x
x = 11