this has already been solved but can someone go over the process? thank you

Babble, Inc., buys 405 blank cassette tapes per month for use producing foreign language courseware. The ordering cost is $18.50. Holding cost is $0.35 per cassette per year. a. How many tapes should Babble order at a time? Babble should order 717 tapes at a time. (Enter your response rounded to the nearest whole number) b. What is the time between orders? The time between orders is 18 months (Enter your response rounded to one decimal place.) Question is complete L Type here to search