4. High-Low Method: Using the information below and the high-low method, estimate the fixed cost and the variable cost of shipping, resulting in the cost formula for shipping expense. Total Shipping Expense $1,800 $2,300 $1,700 $2,000 $2.300 $2,700 $1,200 Units Shipped Month 3 January February March April May June 6 4 5 7 2 July Using the above information, what if 9 units were shipped in August