What is the derivative of the function

$()=62326$f$($x$)=6$x$23$x$26$x$?$

Select one:

a$.$

$126612$x$6$x$6$

b$.$

$12+6612$x$+6$x$6$

c$.$

$12+63612$x$+6$x$36$

d$.$

$12+63+6$