A company selling widgets has found that the number of items sold, x, depends upon the price ...

 A company selling widgets has found that the number of items sold, x, depends upon the price, p at which they're sold, according the equation x=80000/sqrt2p+1. Due to inflation and increasing health benefit costs, the company has been increasing the price by $4 per month. Find the rate at which revenue is changing when the company is selling widgets at $200 each .. in dollars per month?