In Robert's manufacturing plant, the estimated monthly overhead cost function is provided in the Y=m(X)+b format: Total monthly overhead costs =$1.15 (number of machine hours) + $6,500. Given this cost function, specify (a) the variable cost, (b) the fixed cost, (c) the cost driver, and (d) whether these monthly overhead costs are considered variable, fixed, or mixed in total. (Round variable cost to 2 decimal places, e.g. 15.25.) Variable cost Fixed cost Cost driver Cost type