Determine how many gallons (in whole numbers) should be ordered each time to minimize the annual total costs in the following scenario. The item cost per gallon is $7.5, variable costs of storing one gallon in inventory per year amount to 25% of the item cost, paperwork and shipping costs for placing an order are $100 per order, and the demand is fixed at 500 gallons per month.

Refer to information in the above question. If it takes 6 days for the order placed to arrive, at what level of inventory should the product be reordered, assuming a 30-day month (i.e what's the reorder point)?

A: 83 gallons

B: 100 gallons

C: 500 gallons

D: 537 gallons

E: None of the above