1. Convert the annual interest rate into a decimal:
r = 6\% = 0.06
2. Convert the time Margo will borrow the money into years:
t = \frac{10}{12} \text{ years}
3. Plug the values into the simple interest formula:
I = 400 \cdot 0.06 \cdot \frac{10}{12}
4. Calculate the interest:
I = 20
Therefore, Margo will pay $20 in interest.