Penny, Inc. employs a process costing system. Direct materials are added at the beginning of the process. Here is information about July's activities:

On July 1:
Beginning inventories	850 units, 60% complete
Direct materials cost	$5,000
Conversion costs	$4,000
During July:
Number of units started	15,000
Direct materials added	$155,000
Conversion costs added	$83,520
On July 31:
Ending inventories	1,600 units, 40% complete

Using the FIFO method, the cost per equivalent unit for materials used during July was

a. $9.78

b. $10.33

c. $10.78

d. $10.65