Let the two equal interior angles of the isosceles triangle be x and x.
Then, the corresponding exterior angles are 180 - x and 180 - x.
It is given that the sum of the exterior angles is 240°.
Therefore, (180 - x) + (180 - x) = 240
360 - 2x = 240
360 - 240 = 2x
2x = 120
x = 60°
Hence, the measures of each interior angles is 60°.
