Coronado Company uses the FIFO method to compute equivalent units. It has $4200$ units in beginning work in process, $20\%$ complete as to conversion costs and $50\%$ complete as to materials costs, $65700$ units started, and $6300$ units in ending work in process, $30\%$ complete as to conversion costs, and $80\%$ complete as to materials cost. How much are the equivalent units for materials under the FIFO method?

$65700$

$69900$

$68640$

$66540$