Question 1129690
You can think about A and B questions, after looking at question C.


{{{y=a*b^(x/3)}}}
-
x=3 corresponds to 3 years of time.
{{{x/3}}} corresponds to one of these three-year periods, for which 81% of the value is retained.  (19% of value is lost).
{{{y=13000(0.81)^(x/3)}}}