The estimated cost of ending inventory using the gross profit method is $30,600 based on the inventory data from the question above. First, you have to find the cost of good sold from by subtracting the net sales by the gross profit ($29,400=$49,000-40%*$49,000). Then you can use the cost of good sold formula to find the ending inventory's cost ($30,600=$18,000+$42,000-$29,400).