Suppose that

f$($x$)=3$xsqrt$(4$x$^(2)+1)$

$($A$)$ Find all critical values of f$.$ If there are no critical values, enter None. If there are more than one, enter them separated by commas.

Critical value$($s$)=$

$($B$)$ Use interval notation to indicate where f$($x$)$ is increasing.

Increasing:

$($C$)$ Use interval notation to indicate where f$($x$)$ is decreasing.

Decreasing:

$($D$)$ Find the x$-$coordinates of all local maxima of f$.$ If there are no local maxima, enter None. If there are more than one, enter them separated by

commas.

Local maxima at x$=$

$($E$)$ Find the x$-$coordinates of all local minima of f$.$ If there are no local minima, enter None. If there are more than one, enter them separated by

commas.

Local minima at x$=$

WHAT IS LETTER C BECAUSE I KEEP PUTTING NONE BUT IT KEEPS SAYING WRONG ;(