If Margo borrows $600 and agrees to pay it back with 6% annual interest after 6 months, then the amount of interest she will pay can be calculated using the simple interest formula:
I = P * r * t
where:
I = interest
P = principal (the amount borrowed)
r = annual interest rate (as a decimal)
t = time (in years)
Since Margo is paying back the loan after 6 months, or half a year, we need to divide the annual interest rate by 2 to get the rate for 6 months:
r = 6% / 2 = 0.06 / 2 = 0.03
Now we can plug in the values:
I = $600 * 0.03 * (6/12) = $9
Therefore, Margo will pay $9 in interest when she pays back the $600 loan after 6 months at 6% annual interest.