Let [tex] x = m\angle B [/tex]. "The measure of angle A is three times the measure of angle B." So [tex] m\angle A = 3x [/tex].
The angles are supplementary. What does that word mean? Their measures add up to 180 degrees.
[tex] 3x+x=180 \\ 4x = 180 \\ x = 45^\circ [/tex]
The measure of angle A is 3(45) = 135, and the measure of angle B is 45.
