For the last eight months of 2009, Jo Company incurred the following activity levels and Shipping Department Costs:

Month Number of Shipments Shipping Department Costs May 1,800 $14,700 June 1,900 15,200 July 1,700 13,700 August 1,600 14,000 September 1,500 14,300 October 1,300 13,100 November 1,100 12,800 December 1,500 14,600

(a) What is the variable cost per shipment ? Why ? (b) What is the fixed costs per month ? (c) What linear formula may be used to estimate shipping costs ? (d) What is the estimated shipping costs in a month with 2,000 shipments ? Why ?