Smith Corporation wants to find an equation to estimate some of their monthly operating costs for the operating budget for 2021. The following cost and other data were gathered for 2020:

Month	Maintenance Costs	Machine Hours	Health Insurance	Number of Employees	Shipping Costs	Units Shipped
January	$4,510	170	$8,570	63	$28,240	7,060
February	$4,473	110	$8,570	73	$32,920	8,230
March	$4,660	239	$8,570	89	$31,600	7,900
April	$4,870	304	$8,570	102	$25,760	6,440
May	$5,120	459	$8,570	84	$23,760	5,940
June	$4,745	285	$8,570	85	$36,960	9,240
July	$4,927	338	$8,570	88	$34,800	8,700
August	$4,916	363	$8,570	80	$33,720	8,430
September	$5,055	429	$8,570	90	$26,960	6,740
October	$5,226	476	$8,570	101	$28,440	7,110
November	$5,370	500	$8,570	91	$22,000	5,500
December	$4,795	281	$8,570	101	$38,400	9,600

1. Which of the preceding costs is variable? Fixed? Mixed? Explain.

2. Using the high-low method, determine the cost function for each cost.

3. Combine the preceding information to get a monthly operating cost function for the Smith Corporation.

4. Next month, Smith expects to use 350 machine hours, have 90 employees, and ship 8,600 units. Estimate the total operating cost for the month.