Sue Smith owns a $300$ unit tax credit property. She received a total credit allocation covering $200$ of her units and committed to the $20\%$ @ $50\%$ minimum set aside. To earn the maximum possible tax credit, how many units should Sue rent to residents with income no greater than $50\%$ of the area median?

A$.60$ units

B$.100$ units

C$.200$ units

D$.300$ units