The general form of an exponential equation for growth is
and for decay is
In general, if the number inside the parenthesis (the growth or decay rate) is greater than 1, it's a growth problem. If the number inside the parenthesis is greater than 0 but less than 1 (in other words a positive fraction), it's a decay problem.
I’m pretty sure $1,800 Because if you subtract 660 by 470 you get 190 and it you multiply 190 by 6 years you get 1140 and if you add 1140 and 660 you get 1,800