Part A:
Let x=the measure of angle B
4x=180
Explanation: Since angle A and angle B are supplementary they equal 180 degrees. Since angle A is 3 times the measure of angle B you can represent angle A as 3x and angle B as x. Therefore 3x+x=180 and once simplified that equation is equal to 4x=180
Part B:
Angle A=135°
Angle B=45°
Step-by-step explanation:
You can use the equation 4x=180 to find that x=45. Since angle B is equal to x, the measure of angle B is 45 degrees. Since angle A is 3 times the measure of angle B, you can multiply 45 by 3 to get 135 which is the measure of angle A