Exercise $4.$ Find the value$($s$)$ of a and $b$ where the function

$f(a,b)={\displaystyle \underset{a}{\overset{b}{}}}(-2x^2+10x-12)dx$

has a local maximum.

Exercise $5.$ Let $D$ be a region on the $xy-$plane. Let $S$ be the part of the plane $4x-6y+2z=5$ which lies above or below the region $D,($i$.$e$.$ points on the plane $4x-6y+2z=5$ with $(x,y)$ in $D).$ If the area of $S$ is $11,$ find the area of $D.$

Exercise $6.$ Set up a triple iterated integral that would determine the volume of the solid region below $z=x^4+y^4+4$ and above the triangular region on the $xy-$plane with vertices $(-2,0),(2,0),$ and $(0,2).$ Do not evaluate this integral.

SOLVE ALL FOR CALCLUS$3$ PLEASE