Assume that product Z is made of two units of A and four units of B. A is made of three units of C and four of D. D is made of two units of E. Lead times for purchase or fabrication of each unit to final assembly are: Z takes two weeks; A, B, C, and D take one week each; and E takes three weeks. Fifty units are required in period 10. (Assume there is currently no inventory on-hand of these items.) a) Show the bill-of-materials (product structure tree) b) Develop an MRP planning schedule showing gross and net requirements and order release and order receipt dates.