Required information [The following information applies to the questions displayed below.] Phillips Company manufactures air-conditioning units for commercial buildings and has noticed considerable variation in shipping expenses from month to month as per the data below: Month January February March April May June July Units Shipped 4 4 5 2 3 6 8 Total Shipping Expense $ 1,600 $ 2,500 $ 1,850 $ 1,200 $ 1,740 $ 2,100 $ 2,880 4. What is the cost formula for shipping expenses? X