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AC = 36

Step-by-step explanation:

since these triangles are similar, we can use the triangle similitary theorem. This means that the sides are proportional to each other.

ef/bc = 5/45 (1/9) = ed/ba =  2/18 (1/9)

we can see the sides are in a ratio of 1:9, and plug it in the proportion

df/ac = 1/9

4/ac = 1/9

cross multiply and we get that ac = 36

(x) - (y) = (1 + 4i)

2y+y=5

add 2y and y