To answer this question we will use the following formula to compute the x% of y:

Since you have to repay with 3% interest, then you have to pay 103% of the original amount.
The 103% of 260 is:

Now, notice that the interest is the difference between the original amount and the above result:

Answer:
How much will you have to repay? $267.80.
How much of that was of interest? $7.80.