Find the area of the region enclosed by the curve $y = 3 \sqrt { x - 9 }$, the tangent line to this curve at the point $( 18,9 )$, and the $x$-axis. [4 points]
Find the area of the region enclosed by the curve $y = 3 \sqrt { x - 9 }$, the tangent line to this curve at the point $( 18,9 )$, and the $x$-axis. [4 points]