The first step is to calculate the inventory turnover ratio.
Inventory Turnover Ratio = Cost of Goods Sold / Average Inventory Balance
$800,000 / $80,000 = 10.0
Then, take the number of days in the year and divide it by the inventory turnover ratio.
365 / 10.0 = 36.5 Days
Typically, that's how long you'll have to store inventory before selling it to the customer.