Since it decreases by 8 % each year
First, we will find 8% of 4000 km²
8% x 4000km²
8 /100 x 4000km²
8 x 40km²
= 320km²
This implies the area decreases by 320 km² each year
In 9 years the area will decrease by 320 x 9 = 2880km²
The area of the forest after 9years = 4000km² - 2880km² = 1120 km²