Answer:
∠A=-4X+170°
Step-by-step explanation:
IN triangle some of all the angle is 180°
hence in triangle ABC
∠A+∠B+∠C=180°
GIVEN ∠A=X+20° ∠B=3X-10°
HENCE ∠A+3X-10°+X+20°=180°
∠A+4X+10°=180°
