You can put this solution on YOUR website! There are 180 degrees in a triangle. If you want a 1:2:3 ratio, you're talking about 6 equal parts (1+2+3). So:
180/6 = 30
Each "part" of the ratio is equal to 30 degrees. So:
1:2:3 =
30 : 30+30 : 30+30+30 or
30:60:90