Find the Requested Composition of Functions $f ( x ) = x ^ { 2 } + 9$

Multiple Choice

Find the requested composition of functions.
-Given $f ( x ) = x ^ { 2 } + 9$ and $g ( x ) = x ^ { 2 } - 9$ , find $f \circ g ( x )$ .

A) $x ^ { 4 } - 18 x ^ { 2 } + 72$
B) $x ^ { 4 } - 18 x ^ { 2 } + 90$
C) $x ^ { 4 } + 18 x ^ { 2 } + 72$
D) $x ^ { 4 } + 18 x ^ { 2 } + 90$