Find the measure of an angle such that the sum of the measures of its complement and its supplement is 150 degrees?

Very simple, let's mount a linear system: x=measure of the angle; y=supplement; z=complement: I:x+y= 180; II:x+z= 90; III: y+z= 150; Summing I with II we have: I+II: 2x+y+z= 270; III: y+z=150 Now, subtracting III from I+II we have a simple equation: 2x=120; >x= 60< So, the angle whose sum of the measures of its complements and supplement is 150, has 60 degrees.