The sum of all the angles of a triangle = 180⁰
One of the three angles is = 80⁰
=> Sum of the other two angles = 180⁰ - 80⁰ = 100⁰.
Let the two angles be 2x/5 & 3x/5
then, (2x/5 + 3x/5) = 100⁰
=> (5x/5) = x = 100⁰.
Hence the measurement of other two angles are:
2x/5 = 2 × 100⁰/5 = 40⁰, and
3x/5 = 3 × 100⁰/5 = 60⁰