Kindly solve the math

Upon closer inspection, the supplier determines that the demand for a spare pert is normally distributed with mean 4 nos per day and standard deviation 3 nos per day. (The supplier is open 300 days per year.) It usually takes about 4 days to receive an order from the factory. I. What is the standard deviation of usage during the lead time? II. Determine the reorder point needed to achieve a service level of 90 percent. III. What is the safety stock? What is the holding cost associated with this safety stock? IV. How would your analysis change if the service level changed to 95 percent