Write the Surface Area S of a Cube as a Function

Multiple Choice

Write the surface area S of a cube as a function of the length x of one of its edges, and use it to find the surface area (in square inches) when $x = 5$ inches.

A) $S ( 5 ) = 25$ square inches
B) $S ( 5 ) = 750$ square inches
C) $S ( 5 ) = 30$ square inches
D) $S ( 5 ) = 100$ square inches
E) $S ( 5 ) = 150$ square inches