Recent maintenance costs of Divers Corporation are listed below: Machine-Hours Maintenance Costs February 527 $ 5,144 March 499 $ 5,033 April 542 $ 5,220 May 541 $ 5,196 June 489 $ 4,973 July 543 $ 5,200 August 558 $ 5,288 September 513 $ 5,060 Management believes that maintenance cost is a mixed cost that depends on machine-hours. Using the least-squares regression method, the estimate of the variable component of maintenance cost per machine-hour is closest to: