​Average Costs

Multiple Choice

​Average costs.Suppose the average costs of a mining operation depend on the number of machines used,and average costs,in dollars,are given by , ,where x is the number of machines used.How many machines give minimum average costs? ​

A) ​Using 14 machines gives the minimum average costs.
B) ​Using zero machines gives the minimum average costs.
C) ​Using 24 machines gives the minimum average costs.
D) ​Using 28 machines gives the minimum average costs.
E) ​Using 33 machines gives the minimum average costs.