Inacio Corporation uses the weighted-average method in its process costing system. Data concerning the first processing department for the most recent month are listed below:

Beginning work in process inventory:
Units in beginning work in process inventory 2,000
Materials costs $ 14,100
Conversion costs $ 6,200
Percent complete with respect to materials 75 %
Percent complete with respect to conversion 20 %
Units started into production during the month 10,700
Units transferred to the next department during the month 9,600
Materials costs added during the month $ 173,200
Conversion costs added during the month $ 243,200
Ending work in process inventory:
Units in ending work in process inventory 3,100
Percent complete with respect to materials 90 %
Percent complete with respect to conversion 30 %
The cost per equivalent unit for materials for the month in the first processing department is closest to:

a. $13.17
b. $14.11
c. $12.86
d. $15.12