Hendrix, 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 $=750$ units, $60\%$ complete

Direct materials cost $=$$$5,925$

Conversion costs $=$$$4,095$

During July: $,15,000$ units started

Direct materials added $=$$$150,000$

Conversion costs added $=$$$83,520$

On July $31$:

Ending inventories $=1,500$ units, $40\%$ complete

Using the FIFO method, the number of units started and completed in July was

a$)14,250$

b$)15,000$

c$)13,500$

d$)15,750$