Dubbo Ltd has accumulated the following data for the most recent 6-month period. Maintenance services have been determined to be a mixed cost. Month Direct labour hours Maintenance services July 25,000 $45,000 August 18,000 28,000 September 21,000 40,000 October 6,000 13,000 November 12,000 20,000 December 9,000 20,000 Management believes that maintenance cost is a mixed cost that depends on direct labour hours. Using the high-low method to estimate the variable component of this cost, the estimate would be closest to: Select one: a. $0.69 per direct labour hour b. $0.59 per direct labour hour c. $1.68 per direct labour hour d. $1.60 per direct labour hour