Phillips Company manufactures air-conditioning units for commercial buildings and has noticed considerable variation in shipping expenses from month to month as per the data below:

	Units	Total Shipping
Month	Shipped	Expense
January	4	$	1,600
February	4	$	2,500
March	5	$	1,850
April	2	$	1,200
May	3	$	1,740
June	6	$	2,100
July	8	$	2,880

7. If 10 air conditioners are shipped in October, estimate the variable shipping expense.