### The average income of A, B and C is Rs. 12,000 per month and average income of B, C and D is Rs. 15,000 per month. If the average salary of D be twice that of A, then the average salary of B and C is in Rs. :

A. 8,000

B. 18,000

C. 13,500

D. 9,000

$\begin{array}{l}A+B+C=12000\times3\\ B+C+D=15000\times3\\ \rightarrow D-A=3000\times3=9000\\ \text{ Also, }D=2A\\ \text{ Then, }D=18000\text{ and }A=9000\\ \text{Therefore},\\ \text{Average salary of B and C}\\ =\Large\frac{45000-18000}{2}\\ =13500\end{array}$