Question

Angle A and angle B are supplementary angles, if angle B equals 73°, what is the measurement of angle A?

Answer 1

Supplementary means adds to 180
A+B=180
B=73
A+73=180
minus 73 both sides
A+73-73=180-73
A+0=107
A=107

A=107 degrees

Answer 2

Supplementary angles equal to 180 degrees. 

So you can set up an equation and have x be the measure of Angle A. 

73 + x = 180

Solve for x. 
x = 107