Total number of degrees in a triangle = 180 degrees.
180 - 57 = 123 degrees left.
73.5 (possible x value) - 24 = 49.5
73.5 degrees + 49.5 degrees = 123 degrees
x = 73.5
x must equal 73.5 degrees, for when you subtract 24 from 73.5, you get 49.5. When you add up all of the angle values, you get 57 + 73.5 + 49.5 = 180.