Answer
(a) $66661.21\ dollars$ and $9881.21\ dollars$
(b) $86416.98\ dollars$ and $29636.98\ dollars$
Work Step by Step
Given $P=56780, r=0.028$, we have:
(a) $n=4, t=\frac{23}{4}\ yr$, the future value $A=P(1+\frac{r}{n})^{nt}=56780(1+\frac{0.028}{4})^{4(\frac{23}{4})}\approx66661.21\ dollars$ and the interest $I=A-P=9881.21\ dollars$
(b) the future value $A=Pe^{rt}=56780e^{0.028(15)}\approx86416.98\ dollars$ and the interest $I=A-P=29636.98\ dollars$
