Demand during lead time $(10$ days$)$ for lamps at one of GE Lighting warehouses near Paris is normally distributed with average $20,000$ and standard deviation $5000.$ The demand is estimated at an average rate of $2000$ units per day, and the warehouse carries a safety inventory of $4000$ units.

$-$ Determine the service level of the warehouse.$-$ What would be the safety stock if the service level was to

increase to $85\%,90\%$ and $95\%?$