Consider the EOQ with backlogged demand model. If the optimal policy is used, deter$-$

mine the following in terms of $K,c,,h,l,$ and $Q^{**}$ only:

$($a$)$ The average time that a demand waits to be filled. $[$Including demands that are

filled instantaneously.$]$

$($b$)$ The average time that a part spends in on$-$hand inventory. $[$Including parts that

spend time $0$ in on$-$hand inventory.$]$