'Can anyone quickly explain what is a difference between 75-a and the question below? For 75-a, the answer is f'(10) but the question below gets the answer of c'(12) as the tutor replied to my question with an answer of c'(12). Why isnt should be c'(10) like as the same way of 75-a? Isnt 75-a should get the answer of f'(11) then?

Suppose the cost in dollars of manufacturing x units of cat toys is given by the equation C(x) = 120*/2 - 4x2. Suppose the current level of production is 10 units of cat toys. Use marginal analysis to estimate the change in the total cost if 12 units are produced instead. answer correct to 3 decimals75. MARGINAL ANALYSIS Jane McGee, the mathematics editor at a major publishing house, estimates that if x thousand complimentary copies are distributed to professors, the rstyear sales of a certain new text will be f(x) = 20 15602" thousand copies. Currently, Jane is planning to distribute 10,000 complimentary copies. 3. Use marginal analysis to estimate the increase in rst-year sales that Jane should expect if 1,000 additional complimentary copies are distributed. b. Calculate the actual increase in rstyear sales that will result from the distribution of the additional 1,000 complimentary copies. Is the estimate in part (a) a good one