The answer is .06x * 2000, then you would subtract the number that results from this equation from the 2000 to get the area of the forest each year.
For example:
Let’s suppose that it is 3 years from the initial decrease. Let’s plug this into the equation.
.06(3) * 2000 = 360
Then you would take that 360 and subtract it from the 2000 to get the total area that is left
2000 - 360 = 1640 square km
Hope this helps!