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: Total Units Shipping Month Shipped Expense January 4 $1, 800 February $2, 700 March $2 , 100 April OWNUP $1, 230 May $1, 890 June $2, 400 July $3, 360 Required: 1. Which two months should be used if Phillips wants to estimate the behaviour of shipping expenses using the high-low method? Month Shipping Expense High activity level $ 3,360 Low activity level $ 1,230