SnuggleSoft Pillow Co$.$ sees a weekly demand for $120$ of their memory foam pillows, with a lead time of $3$ weeks for new materials. They maintain a safety stock of $180$ pillows for an $85\%$ service level, with a standard deviation of $40$ pillows. What is the reorder point for their fluffy inventory? a$)540$ units b$)600$ units c$)580$ units d$)720$ units