Write an Expression for the Volume and Simplify Your Answer $3 x ^ { 3 } + 15 x + 12$

Multiple Choice

Write an expression for the volume and simplify your answer.
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A) $3 x ^ { 3 } + 15 x + 12$
B) $3 x ^ { 3 } + 15 x ^ { 2 } + 12 x$
C) $3 x ^ { 3 } + 12 x$
D) $x ^ { 3 } + 5 x ^ { 2 } + 4 x$