A $100,000 mortgage is taken out at 8% compounded semi-annually, to be amortized over 25 years by monthly payments. Payments are rounded up to the next 5 dollars and the final payment is reduced accordingly.

1. Suppose extra payments are made at the end of every year to get the mortgage paid off sooner. Determine the time and amount of the last payment on the mortgage if the extra payments are: $300 at the end of year 1; $350 at the end of year 2; $400 at the end of year 3, $450 at the end of year 4, ... (Increasing by $50 each year).