Find the Value of X for Which the Marginal Profit $C ( x ) = 2 x , R ( x ) = 6 x - \frac { x ^ { 2 } } { 1,000 }$

Multiple Choice

Find the value of x for which the marginal profit is zero.
$C ( x ) = 2 x , R ( x ) = 6 x - \frac { x ^ { 2 } } { 1,000 }$

A) $x = 3,000$
B) $x = 4,000$
C) $x = 2,000$
D) $x = - 2,000$
E) $x = 1,000$