Answer
$6.12\%$
Work Step by Step
Let the required interest rate be $r$, given $P=1500,A=1800,t=3,n=4$. We have $1800=1500(1+\frac{r}{4})^{4(3)} \longrightarrow 1+\frac{r}{4}=(\frac{18}{15})^{1/12} \longrightarrow r=4((\frac{18}{15})^{1/12}-1)\approx0.0612$ or $6.12\%$
