The following information is available for a company's cost of sales over the last four months. Month Units Sold Total Costs January 500 $ 35,000 February 900 $ 42,000 March 2,100 $ 54,000 April 2,900 $ 66,000 Using the high-low method, the estimated variable cost of sales per unit sold is:

a.$22.76.

b.$70.00.

c.$29.71.

d.$12.92.

e.$25.71.