Involve the average cost of manufacturing a quantity $q$ of a good, which is defined to be.
The average cost per item to produce $q$ items is given by
\[
a(q)=0.01 q^{2}-0.6 q+13, \text { for } q>0
\]
(a) What is the total cost, $C(q),$ of producing $q$ goods?
(b) What is the minimum marginal cost? What is the practical interpretation of this result?
(c) At what production level is the average cost a minimum? What is the lowest average cost?
(d) Compute the marginal cost at $q=30 .$ How does this relate to your answer to part (c)? Explain this relationship both analytically and in words.