Kavya starts writing code for an app on her own; she could finish it alone in 24 days. After 6 days, Rohan joins her; he could finish the whole app alone in 12 days. How many days after Rohan joins is the app finished?

Explanation

1. 01

   In 6 days Kavya does $\frac{6}{24} = \frac{1}{4}$ of the app, leaving $\frac{3}{4}$.

2. 02

   Together: $\frac{1}{24} + \frac{1}{12} = \frac{3}{24} = \frac{1}{8}$ per day.

3. 03

   Time for $\frac{3}{4}$: $\frac{3}{4} \div \frac{1}{8} = 6$ days.