Tony-Bliar Company uses a weighted-average perpetual inventory system.
-  May 2: 8 units were purchased at $12 per unit.
-  May 18: 13 units were purchased at $13 per unit.
-  May 29: 12 units were sold.
-  May 31: 12 units were purchased at $15 per unit.
What is the per-unit value of ending inventory on May 31?