A product currently sells for $40 a unit and the sales of this product currently average at 210 units a month.For every $2 dollar increase in the per unit price of this product, the sales drop by an average of 6 units a month.Conversely, for every $2 dollar decrease in the per unit price of this product, the sales increase by an average of 6 units a month. Express the average monthly revenue,R, from the sales of this product as a function of the per unit pricep.