Answer :
Explanation :

As the ratio of their present ages is 3 : 4 , let their present ages be 3X and 4X. So, 5 years ago, as the ratio of their ages was 5 : 7, we can write  (3x-5) : (4x-5) = 5 : 7. Solving, we get X = 10. Hence, their present ages are 3X = 30 and 4X = 40