The total cost function for a product is

C$($x$)=675$ ln$($x $+10)+1700$

where x is the number of units produced.

$($a$)$ Find the total cost of producing $100$ units. $($Round your answer to the nearest cent.$)$

$

$($b$)$ Producing how many units will give total costs of $$6500?($Round your answer to the nearest whole number.$)$

units