The following table lists the components needed to assemble an end item, lead times, and quantities on hand.

Item End B C D E F G H

LT $($week$)12331212$

Amount on hand $0101025123050$

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a$.$ If $21$ units of the end item are to be assembled, how many additional units of E are needed? $($Hint: You don't need to develop an MRP plan to determine this.$)$

b$.$ An order for the end item is scheduled to be shipped at the start of week $13.$ What is the latest week that the order can be started and still be ready to ship on time? $($Hint: You don't need to develop an MRP plan for this part either.$)$