Big Box Store has operated with a 30% average gross profit ratio for a number of years. It had $100,000 in sales during the second quarter of this year. If it began the quarter with $18,000 of inventory at cost and purchased $72,000 of inventory during the quarter, its estimated ending inventory by the gross profit method is:

$30,000.

$21,000.

$20,000.

$18,000.

$27,000.