The Rapid Delivery Service is considering the expansion of its business into afternoon retail delivery service. This would require an additional $40,000 in labor costs per month. Company-owned vehicles now used to make morning deliveries to local manufacturers could be used in the afternoons to make retail deliveries. However, it is estimated that an additional $11,500 would be required per month for gas, oil, and maintenance. It is further estimated that the retail delivery use of the trucks would be allocated 40% of the existing $14,500 fixed vehicle costs. What is the differential delivery cost per month for expanding into the retail delivery market