3. Write a linear cost function equation for each of the following conditions. Use y for estimated costs and X for activity of the cost driver. (4 points) a. Direct materials cost is $2.70 per pound b. Total cost is fixed at $800 per month regardless of the number of units produced. c. Auto rental has a fixed fee of $90.00 per day plus $1.75 per mile driven. d. Machine operating costs include $1,000 of maintenance per month, and $15.00 of coolant usage costs for each day the machinery is in operation