Shishir borrowed some money from a bank with 6 p.c.p.a simple interest for the first three years, 8 p.c.p.a for the next 4 yrs and 12 p.c.p.a for the period beyond seven years. If at the end of twelve years, he pays a total interest of Rs. 6,600, how much money did he borrow from the bank?

• A. Rs. 6,000
• B. Rs. 12,000
• C. Rs. 8,000
• D. Rs. 9,000