Solve
-The Cost in Millions of Dollars for a Company $x$

Multiple Choice

Solve.
-The cost in millions of dollars for a company to manufacture $x$ thousand automobiles is given by the function $C ( x ) = 5 x ^ { 2 } - 30 x + 81$ . Find the number of automobiles that must be produced to minimize the cost.

A) 3 thousand automobiles
B) 36 thousand automobiles
C) 15 thousand automobiles
D) 6 thousand automobiles