Answer:
External angle= 110º
Step-by-step explanation:
Sum of all angle of triangle = 180º
First you need to find t
t= 50 (see image below)
External angle ( the angle outside next to (t+20))
External angle + (t+20)= 180
External angle + 50+ 20= 180
External angle + 70 = 180
External angle= 110º
