Product a is an end item and is made from two units of b and four of c. b is made of two units of d and two of e. c is made of two units of f and two of e. a has a lead time of one week. b, c, and e have lead times of two weeks, and d and f have lead times of three weeks. if 120 units of a are required in week 10, develop the mrp planning schedule, specifying when items are to be ordered and received. there are currently no units of inventory on hand.