Local bank has a local subsidiary, which requires $75,000 cash every month. It uses $safe armored trucks service for cash delivery. Service company charges $480 for each delivery.

In order to send cash to its subsidiary, the bank has to liquidate part of its securities portfolio which generates 15% annual return.

How many armored truck service trips PER YEAR should the bank order?

(Hint: The annual rate of return in this question is given as 12 * actual monthly rate of return. You can round off to the nearest whole number, for example if your answer is 17.62, you can answer 18.)