using the fixed$-$time period inventory model, and given an average daily demand of $15$ units, $3$ days between inventory reviews, $1$ day for lead time, $20$ units of inventory on hand, a service probability of $98$ percent $($z $=2\mathrm{.}055),$ and a standard deviation of daily demand is $3$ unit, which of the following is the correct order quantity? $-$about $30\mathrm{.}4-$about $52\mathrm{.}3-$about $42\mathrm{.}3-$about $56\mathrm{.}8$