The Marginal Cost of Producing the Xth Box of Computer $2 + \frac { x ^ { 2 } } { 120,000 }$

Multiple Choice

The marginal cost of producing the xth box of computer disks is $2 + \frac { x ^ { 2 } } { 120,000 }$ and the fixed cost is $120,000. Find the cost function $C ( x )$ .

A) $C ( x ) = 2 x + \frac { x ^ { 3 } } { 360,000 } - 120,000$
B) $C ( x ) = 2 x + \frac { x ^ { 3 } } { 360,000 } + 120,000$
C) $C ( x ) = - 2 x + \frac { x ^ { 3 } } { 360,000 } + 120,000$
D) $C ( x ) = \frac { x ^ { 3 } } { 360,000 } - 120,000$
E) $C ( x ) = \frac { x ^ { 3 } } { 360,000 } + 120,000$