Explain clearly

A lash adjuster keeps the pressure constant on engine valves, thereby increasing fuel efficiency in automobile engines. The relationship between price (p) and monthly demand (D) for lash adjusters made by the Wicks Company is given by this equation: D=(1,700-p)/0.20. What is the demand when total revenue is maximized? The total revenue is maximized when demand is units per month. Hint: Find the optimal value of D at which maximum total revenue occurs by taking the first derivative of the equation for total revenue with respect to D and setting it equal to zero. Recall that total revenue is the product of price and demand. To ensure that revenue is maximized (rather than minimized), the sign of the second derivative must be negative