The following information is available for a company's cost of sales over the last five months. Month Units Sold Cost of Sales January ................................................. 400 31,000 February ............................................. 800 37,000 March..................................................... 1,200 43,000 April ....................................................... 1,600 49,000 May ........................................................ 2,400 61,000 34. Using the high-low method, the variable cost per unit is ______. 35. For managing expenses, the cost equation is : _____________________.