Anything would be appreciated!

a manufacturer can produce a color pen at a cost of $3. the color pens have been selling for $5 per pen and at this price, consumers have been buying 4,000 pens per month. the manufacturer is planning to raise the price of the pens and estimates that for each $1 increase in the price, 400 fewer pens will be sold each month. at what price should the manufacturer sell the pens to maximize the profit? what is the profit?