Can someone help me with this problem?

Question

the measure of angle A is 12 degrees more than three times the measure of angle B. If A and B are supplementary angles, find the measure of angle A.

Answer 1

the measure of angle A is 12 degrees more than three times the measure of angle B.

   A = 3B + 12

A and B are supplementary angles

   A + B = 180

substitute for A

 (3B + 12 ) + B = 180

  4B + 12 = 180

        - 12   - 12

    4B    =  168

     4           4  

        B = 42

substitute back in original equation

   A = 3B + 12

   A = 3(42) + 12

  A = 126 + 12

   A = 138

 

check: do the two angles make 180^o?

        138 + 42 = 180      yes