Question 762858
If A's age is 5*x, B's age is 7*x.

4 years later, A will be 5*x + 4 years old
4 years later, B will be 7*x + 4 years old

It is given that {{{(5*x + 4)/(7*x + 4) = 3/4}}}

Cross-multiplying

{{{20*x + 16 = 21*x + 12}}}

{{{x = 4}}}

So A's age is 20 and B's age is 28.

Check: In 4 years, A will be 24 and B 32. Ratio will be 3:4.

:)