In Figure 4.4, supply is perfectly inelastic in graph:

In the above figure, if there is a negative relationship between the variables x and y, which of the graphs above can be used to indicate this?

A) Figure A B) Figure B C) Figure C D) both Figure A and Figure C

[Appendix material: calculus required] Suppose total benefits and total costs are given by B(Y) = 150Y ? 10Y2 and C(Y) = 5Y2. Then marginal costs are: 

A. 2.5Y. B. 5Y. C. 10Y. D. 25Y.