The length of x is 33.85 when rounded to the hundredth place.
You can start solving this by using the tangent function.
Tan(Angle) = opposite/adjacent
Since the angle is 28 and the opposite side is 18, we can set adjacent as x and solve.
Tan(28) = 18/x ---> Cross multiply
xTan(28) = 18 ---> Divide by Tan(28)
x = 18/Tan(28)
Which equals roughly 33.85