Let the **first(elder)** and second sisiter be **x** and **y **respectively.

x/y = 4/3........eqn 1

x = y + 3......eqn 2

*Putting x = y + 3 into eqn 1*

We now have (y + 3)/ y = 4/3

4y = 3(y + 3)

4y = 3y + 9

4y - 3y = 9

**y = 9**

__Therefore the __**younger** sister is** 9 years** old.