The interest rate is 3.5%.
EXPLANATION
We substitute the given values into the formula;
[tex]A=P(1+\frac{r}{100})^t[/tex]
to obtain
[tex]6427.35=6000(1+\frac{r}{100})^2[/tex]
We divide through by 6000 to obtain,
[tex]\frac{6427.35}{6000}=(1+\frac{r}{100})^2[/tex]
This implies that,
[tex]1.071225=(1+\frac{r}{100})^2[/tex]
We take the square root of both sides,
[tex]\sqrt{1.071225}=(1+\frac{r}{100})[/tex]
This gives us,
[tex]1.035=(1+\frac{r}{100})[/tex]
Add -1 to both sides of the equation to obtain
[tex]0.035=\frac{r}{100}[/tex]
Multiply through by 100 to obtain;
[tex]r=3.5[/tex]%
[tex]<b>Therefore the rate is 3.5%</b>[/tex]