Zoe is trying to decide how to divide her time between her job as a wedding photographer, which pays $40 per hour for as many hours as she chooses to work, and as a rock collector, in which case her pay depends both on the price of the rocks and the number of them she finds. these are special rocks so they have value! earnings aside, zoe is indifferent between the two jobs. the number of rocks she can expect to find depends on the number of hours she searches: hours per day total rocks per day0 01 72 133 174 205 21a. the marginal cost of spending one hour hunting for rocks is equal to $ .b. if the price per rock is $10 then the marginal benefit of spending one hour hunting for rocks is equal to $ .c. if the price per rock is $20, then her best choice is to spend hours hunting for rocks. d. if the price per rock falls to $10 then her best choice is to spend hours hunting for rocks.