To answer this, you use the formula
where
is the simple interest that builds
is the principal (AKA the amount invested/borrowed)
is the interest rate per year
is the lenght of the loan, in years.
In your situation:
![\begin{aligned}I &= (\$3000)(5 \%/\text{year})(3 \text{ years})\\[0.5em]&= (3000)(0.05)(3)\\[0.5em]&= 450\end{aligned}](https://img.qammunity.org/2022/formulas/mathematics/college/ftn278tc58a5p7g9rs1oev0pm16eow1o91.png)
This means there'd be $450 of simple interest due at the end of 3 years.