Two angles are called supplementary angles if the sum of two angles is 180 degrees and they form a linear pair.
Here we are given than angle P and angle Q are supplementary angles.
Sum of angle P and angle Q will be 180.
Angle P measures 5x and angle Q measures 3x – 12
Adding the two angles,
x=24
Angle P = 5x
Angle P =5*24 =120
Answer: Angle P is 120 degrees.