Answer:
R = 20
Step-by-step explanation:
The sum of measures of angles in triangle is always 180°:
P + Q + R = 180
Q - R = 50 ⇒ Q = 50 + R
P - Q = 20 ⇒ P = 20 + Q = 20 + 50 + R = 70 + R
so:
P + Q + R = 180
70 + R + 50 + R + R = 180
120 + 3R = 180
3R = 180 - 120
3R = 60
R = 60:3
R = 20
