Formula: If 3 numbers are in the ratio of A:B:C and have sum S, then
1st number = S×
2nd number = S×
3rd number = S×
The three angles of a triangle are in the ratio 5:6:7 and have sum 180°, so
1st angle = 180°× = 180° = 50°
2nd angle = 180°× = 180° = 60°
3rd angle = 180°× = 180° = 70°
Edwin