Answer:
a=8
Explanation:
We can use ratios of similar triangles to solve
The smaller triangle has sides a and 12 and the larger triangle has sides a+a+4 and 12+18 which combine to 2a+4 and 30
a 2a +4
--------- = -----------
12 30
Using cross products
30a = 12(2a+4)
30a = 24a +48
Subtract 24a from each side
30a -24a = 24a-24a +48
6a = 48
Divide each sdie by 6
6a/6 =48/6
a =8