At one of its maintenance facilities, National Airlines stocks radar displays that are used in the cockpit of its CityHopper regional jets. While these displays are generally quite reliable, National has a large fleet of CityHoppers and on average, weekly demand for replacements is $1\mathrm{.}4$ displays, and demand follows a Poisson distribution. Lead time for displays is $4$ weeks, and National uses a periodic review order$-$up$-$to policy with a review period of $1$ week and an oder$-$upto$-$level of $10$ displays.