Answer:
The total amount of interest for a 30-year mortgage 8.6%pa and a 20-year with 7.5% pa is $548,855 and $285,628 respectively.
The monthly principal repayment for a 30-year mortgage 8.6%pa and a 20-year with 7.5% pa is $850 and $1,275 respectively, but the total is same as loan amount of $306,000.
Explanation:
The mortgage loan will be $306,000 (= 85% * $360,000)
Assuming the installment is monthly, then the interest and principal on each mortgage is as calculation attached