Answer
(a) See graph, $8.67\%$, 1997.
(b) $-10.343\%$, unreasonable
Work Step by Step
(a) See graph for $r(x)=-0.115x^2+1.183x+5.623$, we can identify a maximum at $r(5.14)\approx8.67$, thus the highest rate is about $8.67\%$ during year 5 or 1997.
(b) For year 2010, $x=2010-1992=18$ and $r(18)=-0.115(18)^2+1.183(18)+5.623=-10.343\%$. This is unreasonable because of the negative rate.
