Let

f$($x$)=6$x$2+$ x $7.$

$($a$)$

Compute the difference quotient of

f$($x$).$

f$($x $+$ h$)$ f$($x$)$h

$=$

$($b$)$

Compute the derivative of

f$($x$).$

f$\text{'}($x$)=$