If the Total Cost of Manufacturing a Commodity Is $C ( x ) = \frac { 1 } { 8 } x ^ { 2 } + 4 x + 200$

Multiple Choice

If the total cost of manufacturing a commodity is $C ( x ) = \frac { 1 } { 8 } x ^ { 2 } + 4 x + 200$ dollars when x units are produced, for what value of x is the average cost the least?

A) 37
B) 38
C) 39
D) 40