Provide an Appropriate Response $V = \frac { 1 } { 3 } h \left( a ^ { 2 } + a b + b ^ { 2 } \right)$

Provide an appropriate response.
-The formula used to find the volume of the frustum of a square pyramid is $V = \frac { 1 } { 3 } h \left( a ^ { 2 } + a b + b ^ { 2 } \right)$ , where $b$ is the length of the base, $a$ is the length of the top, and $h$ is the height. Try to visualize the figure if $a = b = h$ . Calculate the volume if $a = 261$ feet, $b = 261$ feet, and $h = 261$ feet.

A) $17,779,681$ cubic feet
B) $17,779,581$ cubic feet
C) 68,121 cubic feet
D) $17,780,581$ cubic feet