Since the triangle has a right angle you need to use the the trigonometric function cos (theta which is the angle given that isn't 90°) = adjacent / hypotenuse (adjacent is the side close to the angle you're using which is 22° and the hypotenuse is the longest side of the triangle that is in the away from the right angle)
From there you plug in the numbers which now become cos (22°) = 4.2 / x
Then you isolate the x by multiplying it to both sides so it's on the left and divide both sides by cos (22°) which will end you up x = 4.2 / cos (22°)
