The annuity formula is given to be:

where
PV = Present Value
PMT = Periodic Payment
i = Interest Rate
n = Number of Periods
If one is to pay 20% down, the loan percentage will be:

Therefore, the loan amount will be:

The interest rate is 6.6%. The monthly rate will therefore be:

The number of periods over 14 years is gotten to be:

Therefore, we have the following parameters to work with:

To calculate the PMT, we can rewrite the annuity formula to give:

Therefore, we can solve to be:

Therefore, the monthly payment is 230.70.
The amount paid is given to be:

Therefore, the interest paid is:

Therefore, the interest paid is 13,504.