Kai has a mortgage for $422,038.00. The term of the mortgage is 4 years, and the amortization period is 15 years. Kai will make weekly payments and the mortgage rate is r⁽⁴⁾ = 6.750%. The bank offers Kai a flexible repayment plan, so once a year he can miss a payment or make a payment twice as large as usual. Each year, Kai doubles the last payment of the year.

a) How much would Kai owe at the end of the mortgage term if they didn't double any payments?

b) How much does Kai still owe at the end of the mortgage term (including the extra/missed payments)?