E-commerce Inc. provides the following financial information for the past three years.

Description	2021	2020	2019
Sales	$7,000,000	$6,500,000	$6,000,000
Cost of Sales	$4,200,000	$3,900,000	$3,600,000
Gross Profit	$2,800,000	$2,600,000	$2,400,000
Marketing Expenses	$1,400,000	$1,300,000	$1,200,000
Administrative Expenses	$700,000	$650,000	$600,000
Total Operating Expenses	$2,100,000	$1,950,000	$1,800,000
Operating Income	$700,000	$650,000	$600,000
Other Income	$140,000	$130,000	$120,000
Income Before Tax	$840,000	$780,000	$720,000
Tax	$168,000	$156,000	$144,000
Net Income	$672,000	$624,000	$576,000

Requirements:

1. Compute the Gross Profit Ratio for each year.
2. Calculate the Operating Expense Ratio for each year.
3. Determine the Net Profit Margin for each year.
4. Evaluate the company's expense management over the three years.