Answer:
9 : 9 : 21
Explanation:
sum the parts of the ratio, 3 + 3 + 7 = 13 parts
Divide 39 by 13 to find the value of one part of the ratio
39 ÷ 13 = 3 ← value of 1 part of the ratio, then
3 parts = 3 × 3 = 9
7 parts = 7 × 3 = 21
Then 39 in ratio 3 : 3 : 7 = 9 : 9 : 21