If angle P and angle Q are supplementary and the measure of angle P is 60^o, then the measure of angle Q is ________.

When the sum of the measures of two angles is 180^o, then the angles are called supplementary angles.

=> P + Q = 180^o

=> 60^o + Q = 180^o

=> Q = 180^o – 60^o

=> Q = 120^o