$11\mathrm{.}6.$ The standard deviation of demand during the lead time is $100$ units.

Calculate the safety stock required for the following service levels: $75\%,80\%,85\%,90\%,95\%,$ and $99\mathrm{.}99\%.$

Calculate the change in safety stock required to increase the service levels from $75$ to $80\%,80$ to $85\%,85$ to $90\%,90$ to $95\%,$ and $95$ to $99\mathrm{.}99\%.$ What conclusion do you reach?