Wachovia operates the network of automated teller machines (ATMs). On average customer withdrawals $80 of cash each time. Bank evaluates that fixed cost of filling ATM with cash is about $100 regardless of amount of cash put in. Each month on average 600 customers utilize ATM to withdrawal cash. How much cash must bank keep at an ATM if its annual cost of money is 10%? How frequently must bank replenish the ATM?