a) The amount of their monthly repayment for a 20-year loan:
\[ M = 233{,}000 \times \frac{0.0055833 \times (1 + 0.0055833)^{240}}{(1 + 0.0055833)^{240} - 1} \]
\[ M \approx \$1{,}756.89 \]
b) The total amount they would repay by the end of the 20 years:
\[ \text{Total repayment} = M \times 240 \]
\[ \text{Total repayment} \approx \$421{,}653.60 \]
c) What would their monthly repayment be if they paid off the loan over 30 years:
\[ M = 233{,}000 \times \frac{0.0055833 \times (1 + 0.0055833)^{360}}{(1 + 0.0055833)^{360} - 1} \]
\[ M \approx \$1{,}491.60 \]
d) How much do they save each month on their loan repayment if they take a 30-year loan:
\[ \text{Monthly savings} = M_{20} - M_{30} \]
\[ \text{Monthly savings} \approx \$265.29 \]
e) How much extra do they pay in total when paying off the loan over 30 years:
\[ \text{Total repayment for 30 years} = M_{30} \times 360 \]
\[ \text{Total repayment for 30 years} \approx \$536{,}976 \]
\[ \text{Extra payment} = \text{Total repayment for 30 years} - \text{Total repayment for 20 years} \]
\[ \text{Extra payment} \approx \$115{,}322.40 \]