You have calculated, using the high-low method, a variable cost per machine hour of $0.80 for your production power costs. Power costs at 6,000 machine hours are $5,400; at 9,000 machine hours, they are $7,800. What are the total fixed costs that you would use to estimate production power costs for your company at any level within your relevant range? a. $600 b. $6,400 c. $2,400 d. $4,800