Hello Ruby,
Given the ratio of 1:2:3, the actual side measures could be 2:4:6, 3:6:9...some (same) number multiplied by the original three. Let 'x' be that number.
Then, since there are 180 degrees in a triangle, we have
1x + 2x + 3x = 180
→ 6x = 180
→ x = 30
→ the three angles are 30, 60, and 90.
I hope the above helps, and thank you for the question. Have a great morning!
Michael E.