Question

And this is why I hate math.

Answer 1

Complementary angels add up to 90°
so x+18°=90°
so x=90-18=72°

Answer 2

Complementary angles = angles that add up to 90°

So since ∠ABD and ∠DBC are complementary, you just need to add them and equal them to 90; your equation will look like this: $18+x=90$

Just subtract 18 on each side, and your answer will be $x=72$