Industrial Manufacturing Ltd. reports the following financial data for the past three years.

Description	2021	2020	2019
Sales	$18,000,000	$17,500,000	$17,000,000
Cost of Goods Sold	$10,800,000	$10,500,000	$10,200,000
Gross Profit	$7,200,000	$7,000,000	$6,800,000
Operating Expenses	$3,600,000	$3,500,000	$3,400,000
Operating Income	$3,600,000	$3,500,000	$3,400,000
Interest Expense	$720,000	$700,000	$680,000
Earnings Before Tax	$2,880,000	$2,800,000	$2,720,000
Tax Expense	$576,000	$560,000	$544,000
Net Income	$2,304,000	$2,240,000	$2,176,000

Requirements:

1. Calculate the Gross Profit Margin for each year.
2. Determine the Operating Margin for each year.
3. Compute the Net Profit Margin for each year.
4. Discuss the trend in profitability over the three years.