i have a customer who orders the same amount of product every month. he will need 15 extra units next month, 30 extra units the next month, and 15 extra units the third month. After that his needs will drop back to their original level. He wants to know how many extra unit per month to build into his budget above the usual amount over 12 months to cover the three month spike. How many extra units per month should he add to his 12 month budget