Marlo Stanfield's operation also uses large quantities of prepaid cell phones, on average 1500 per week with a standard deviation of 145. The lead time for their own brand of prepaid cell phones is three weeks and they have a lot size of 350 phones. To ensure they never run out, they keep a safety stock of 500 phones with Proposition Joe. What is the standard deviation of demand during lead time?

A) 251 phones

B) 2187 phones

C) 4500 phones

D) 4751 phones

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