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	30	$	1,800
February	60	$	2,300
March	40	$	1,700
April	50	$	2,000
May	70	$	2,300
June	80	$	2,700
July	20	$	1,200

Required: Using the high-low method, calculate the equation of a cost line for the shipping expense for this company (Y = a + bX)