So you have two squares, one with a length of 20 on all sides, and onewith a length of 80 on all sides. It says the 80 one is a sclaed copy of the 20 one, so they took the 20 one and enlarged it to make the 80 one. You would divide 80 by 20 and get 4. This is how much the sides of the 20 one were multipled by to get the 80 one.
So 1000987 in 3 years or 1000987:3 or i like to put it as 1000987:3 we notice that 6 is 2 times of 3 so we just multiply 1000987:3 by 2 and get 2001974:6 2001974 in 6 years