A certain forest covers an area of 2400km^2. Suppose that each year this area decreases by 8.5%. What will the area be after 13 years? ... ?

This is like the equation of a line where y is the area, x is the time, and 8.5% is your slope. So you have y=0.085x+b (reason why I switched 8.5% into 0.085 is because that is how you write a percent as a decimal). So now you need to find what b is. So you know orignally the area is 2400km^2 at x=0 years (this is what it is initially). If you plug those numbers in you have:2400=0.085 (0) + bThen after solving for b, you can write your equation as:y=0.085x + (whatever you found b to be) Then plug 13 in for x and you have your answer. y=-.085 (13) + 2400