In a partnership business, the total profit of A and B is $\text{Rs. }2000$. If the capital of A is $\text{Rs. }6000$ and his profit share is $\text{Rs. }1200$, find the capital invested by B.

1. A
   $\text{Rs. }4000$
2. B
   $\text{Rs. }5000$
3. C
   $\text{Rs. }4500$
4. D
   $\text{Rs. }3000$