When the price for a color television is $240, the average monthly sales for this item at a department store is 450. For each $10 increase in price, the average monthly sales fall by 20 units. What is...

When the price for a color television is $240, the average monthly sales for this item at a department store is 450. For each $10 increase in price, the average monthly sales fall by 20 units. What is the average monthly sales if the price is $400 per color television?