John has USD$240,000$ home loan for $20$ years at a nominal rate of $4\mathrm{.}5\%$

convertible monthly. He makes fixed principal repayment of USD$1000$

each month. Find,

a$.$ his loan balance after $12$ years

b$.$ his ${100}^{th}$ month payment

c$.$ the sum of amount of interest paid in the $5^{th}$ year $($from ${49}^{th}$ month to

${60}^{th}$ month$).$