Remember, SOH CAH TOA for the trigonometric functions. In this problem, we are given an angle, a side opposite that angle, and a side adjacent to that angle. So, we should use the tangent function to find the missing side.
tan(20) = 4 / x
tan(20)x = 4
x = 4 / tan(20)
x = 10.99 units
Hope this helps! :)
