The Sit-N-Spin Corporation manufactures and assembles office chairs. Sit - N - Spin uses an activity-based costing system to allocate all manufacturing conversion costs. Each chair consists of 10 separate parts totaling $145 in direct materials, and requires 6.0 hours of machine time to produce. Additional information follows: Activity Materials handling Machining Assembling Packaging Allocation Base Number of parts Machine hours Number of parts Number of finished units Cost Allocation Rate $3.75 per part $3.00 per machine hour $0.50 per part $4.75 per finished unit What is the cost of machining per chair? O A. $28.50 O B. $18.00 OC. $72.00 OD. $30.00