Answer: The cost of operation was reduced by 21.29%.
Explanation:
Since we have given that
Cost of operation earlier = $21,840 per month
Cost of operation now = $17,190 per month
Difference between them is given by
$21,840 - $17,190
=$4,650
Percentage by which the cost of operation was reduced is given by

Hence, the cost of operation was reduced by 21.29%.