A Bank requires its savings account depositors to maintain a minimum balance of Rs. 6,000. The services offered costs the bank Rs. 4.5 per depositor per month and the bank estimates a monthly cost of Rs. 3.5 per depositor in overhead expenses. The bank requires a minimum profit of Rs. 3 per month on such transactions. It further estimates that it saves about 2% in operating expenses for each Rs. 1500 held as deposits above the minimum balance of Rs. 6,000. What would be the appropriate monthly fee for a customer holding an average minimum balance of Rs. 15,000?