Please explain and show work. This makes no sense to me$.$ The horizontal $x-$axis is drawn through the centroid $C$ of the area shown, and it divides the area into two component areas $A_1$ and $A_2.$

Determine the first moment of each component area with respect to the $x-$axis if $a=0\mathrm{.}3in.$ and $b=0\mathrm{.}9in.$

The first moment of the area above the $x-$axis is

$i{n}^3.$

The first moment of the area below the $x-$axis is $-$

$i{n}^3.$