Given the following data, calculate the gross profit using the average-cost method, if the selling price was $20 per unit.
Date Item Unit
1/1 Beginning inventory 40 units at $12 per unit
3/5 Purchase of inventory 18 units at $14 per unit
5/30 Purchase of inventory 24 units at $18 per unit
12/31 Ending inventory 20 units
A. $851.71
B. $634.78
C. $359.90
D. $283.90