The J. Page Furniture Company has the following information available regarding costs at various levels of monthly production:

Production volume (units)	16,000 Units	22,000 Units
Direct materials	$70,000	$100,000
Direct labor	66,000	90,000
Indirect materials	21,000	30,000
Supervisors salaries	12,000	12,000
Depreciation on plant and equipment	10,000	10,000
Maintenance	32,000	44,000
Utilities	15,000	21,000
Insurance on plant and equipment	1,600	1,600
Property taxes on plant and equipment	2,000	2,000
Total	$229,600	$310,600

Develop an equation for total monthly production costs using the high-low method of cost estimation, and predict total costs for a monthly production volume of 18,000 units.