Margo borrows $100, agreeing to pay it back with 6% annual interest after 6 months. How much interest will she pay.

Okay so she paid 100 dollars. There is 6 percent every month.

100*0.06=6

So, after 1 year it will be at 106 dollars ...

But, we are looking for 6 months which is half of the year.

6/2=3 ...

So she will pay 3 dollars in interest.