P$($x$)=-8$x$^(2)+1750$x$-35000$

$($a$)$ What is the actual profit $($in dollars$)$ realized from renting the $61$ st unit, assuming that $60$ units have already been rented?

$($b$)$ Compute the marginal profit $($in dollars$)$ when x$=60$ and compare your results with that obtained in part $($a$).$

$