9. Fill in the blanks. When choosing the levels of two activities, A and B, in order to maxi- mize total benefits within a given budget: a. If at the given levels of A and B, MB/P of A is MB/P of B, increasing A and decreasing B while holding expenditure constant will increase total benefits. b. If at the given levels of A and B, MB/P of A is MB/P of B, increasing B and decreasing A while holding expenditure constant will increase total benefits. c. The optimal levels of A and B are the levels at which equals