Answer: x = 18
================================================
Work Shown:
We'll use the tangent rule since it connects the opposite and adjacent side.
tan(angle) = opposite/adjacent
tan(42) = x/20
20*tan(42) = x
x = 20*tan(42)
x = 18.00808
x = 18
The value is approximate.
Rounding 18.00808 to the nearest tenth leads to 18.0 which is the same as 18
Make sure your calculator is in degree mode.