Terri had a triangular garden bed in her back yard. The measure of the angle C is 40 degrees less than two times the measure of angle A, and the measurement of angle B is 20 degrees less than the measure of angle A. Find the measures of the three angles. Start your work by defining all the unknown angles in terms of one variable.

a+(a-20)+(2x-40)=180 is the one variable I have come up with.