$4$a$.$ You want to buy a new house, but you are not sure what you can afford. You are nervous about borrowing more than $$180,000.$ What is the monthly payment for a $30-$year loan with a $7\mathrm{.}5\%$ APR if the loan is for $$175,000?$

$4$b$.$ You find a house you really like, but you would have to borrow $$195,000.$ What is the monthly payment for a $30-$year loan with a $7\mathrm{.}5\%$ APR if the loan is for $$195,000?$

$4$c$.$ If you take out a $15-$year mortgage, the interest rate falls to $6\mathrm{.}5\%.$ What is the monthly payment for a $15-$year loan with a $6\mathrm{.}5\%$ APR if the loan is for $$175,000?$