Let us call the angles x, y , and z. We know that these three angles must add up to 180; therefore,

If x is the smallest angle, we know that one of the angles (call it y) is 3 times this angle; therefore,

And the other angle z is 20 more than the smallest angle x; therefore, we have

Putting the last two equations into the very first equation gives us



which is the measure of the smallest angle.
The other two angles are


and


Hence, the measure of the smallest angle is 32,
The measure of the middle angle is 52
And the measure of the largest angle is 96.