Given the figure below, operation $4$ represents a rework operation on parts that fail inspection upon completion of operation $2.$

$2$

$3$

$5000$ Units

d$,=5\%$

d; $=10\%$

d$.=5\%$

d$,=2\%$

How many units must the process start with in order to meet the required output of

$5000$ units?