Archer Company is a wholesaler of custom-built air-conditioning units for commercial buildings. It gathered the following monthly data relating to units shipped and total shipping expense:

Month	Units Shipped	Total Shipping Expense
January	4	$ 1,200
February	7	$ 1,700
March	5	$ 1,100
April	6	$ 1,400
May	8	$ 1,700
June	9	$ 2,700
July	2	$ 600

2. Using the high-low method, estimate the cost formula for shipping expense.