To finance her community college education sarah takes out a loan for $2900. after a year she decides to pay off the interest which is 5% of $2900. how much will she pay

You want to calculate the interest on $2900 at 5% interest per year after 1 year(s).The formula we'll use for this is the simple interest formula, or:
I=P x r x t
Where:
P is the principal amount, $2900.00.
r is the interest rate, 5% per year, or in decimal form, 5/100=0.05.
t is the time involved, 1year(s) time periods.
So, t is 1year time periods.
To find the simple interest, we multiply 2900 × 0.05 × 1 to get that:
The interest is: $145.00