Lacourse Incorporated's inspection costs are listed below: Units Produced Inspection Costs January 647 $ 15,309 February 724 $ 15,965 March 694 $ 15,715 April 645 $ 15,271 May 696 $ 15,745 June 665 $ 15,442 July 718 $ 15,933 August 699 $ 15,739 Management believes that inspection cost is a mixed cost that depends on units produced. Using the least-squares regression method, the estimate of the variable component of inspection cost per unit produced is closest to: