Do you recognize that the hypotenuse here has the length 22 and that the opposite side is the unknown (x)? The angle is 21 degrees.
This is a perfect application of the tangent function:
tan 21 deg = opp / adj = opp / 22 = x / 22
tan 21 deg = 0.384 so x would be 22 tan 21 deg, or
x = 22*(0.384)
= 8.45 (answer)