Hello. Firstly you have to remembet that the sum of the three angles in any triangle is 180grades
So, determining the constant (k) you will have:
2:9:1
2k+9k+1k=180
12k=180 180/12=k
k = 15
Multiply the constant by 180 and divide by the given ratio:
180*15 / 2
180*15 / 9 etc
then your angles are
2:9:1
24:108:12