solve by steps clearly

MRP The product structure tree for end item E follows. The manager wants to know the material requirements for ordered part R that will be needed to complete 120 units of E by the start of week 5. Lead times for items are one week for level 0 items, one week for level 1 items, and two weeks for level 2 items. There is a scheduled receipt of 60 units of M at the start of week 2 and 100 units of R at the start of week 1. Lot-for-lot ordering is used. Level 0 E 1 M(3) 1(2) 2 R(2) N(4)