Let x be the measure of the exterior angle.
In the triangle,
using angle sum property, we have,
t + (t + 10) + (t + 20) = 180
=> t + t + 10 + t + 20 = 180
=> 3t + 30 = 180
=> 3t = 180 - 30
=> t = 150/3
=> t = 50
t° = 50°
(t+10)°= (50 + 10)° = 60°
(t+20)° = (50 + 20)° = 70°
now,
x° = (t+10)° + t° [by exterior angle property]
= 60° + 50°
= 110°
therefore the measure of the exterior angle is 110°
