Question

Write as a proportion 2 is to 5 as 18 is to x

Answer 1

I'd present the problem as an equation of ratios:

2 18
--- = ----
5 x

Then 2x = 90, and x = 45.

Answer 2

2 is to 5 as 18 is to x
18 is 2 x 9
5 x 9 = 45
18:45.