Answer:
so first we will find the interior angle:
1 angle : 31 (given )
2 angle :31 ( the base angles of isoscles triangle are equal)
3 angle : 31 + 31 + x = 180 ( angle sum property of triangle)
x = 180 - 62 = 118
now the exterior angles :
1 angle : 180 - 31 = 149 ( exterior angle and the angle adjacent usually forms a line (= 180) )
2 angle : 149 ( same reason as the first)
3 angle : 180 - 118 = 62 ( same reason as the first)
( i dont know if there is any other way, but this is one)