customer service$)$: $75\%,80\%,85\%,90\%.$ Then calculate the difference between the rates.

$1,200$ units per order $($average$)$

$4,000$ orders per year

Pretax profit per unit $=$$$3$

Pretax profit per order $=$$$3600$

Invoice deduction per order $=$$$450$

Percentage of incomplete orders back$-$ordered is $78\%$

Backorder costs $($per order$)=$$$300$

Percentage of incomplete orders cancelled is $22\%$