Assembly department of Zahra Technologies had $100$ units as work in process at the beginning of the month. These units were $50\%$ complete. It has $200$ units which are $25\%$ complete at the end of the month. During the month, it completed and transferred $500$ units. Direct materials are added at the beginning of production. Conversion costs are allocated evenly throughout production. Zahra uses weighted$-$average process$-$costing method.

The number of equivalent units of work done during the month for direct materials is $\_\_\_\_\_\_\_\_.$

Question $9$ options:

$500$ units

$600$ units

$700$ units

$800$ units

none of the above.