The hypotenuses are 54.5 and 15.
x is the length of the leg between the right angle and the unmarked acute angle. It corresponds to the similar side of the other triangle between the right angle and the unmarked angle, 9.
54.5 is to 15 as x is to 9
54.5/15 = x/9
15x = 54.5 * 9
15x = 490.5
x = 32.7