for the first question:
here is what I did:
EQ#1 -> found partial derivative of M, with respect to c, and set it equal to 0
EQ#2 -> found partial derivative of M, with respect to f, and set it equal to 0
solved this system of equations (EQ#1 and EQ#2) for c and f.
plugged those values into original function to get value of M at this point.
Oh, and all values of c, f, and M should lie between 0 and 1 because they represent the fraction of buyers who would buy the corresponding product again, and this can't be less and 0% or greater than 100%, so if you get a value outside that, you know you made a calculation mistake somewhere. Like your M = 240 example must be wrong, it would mean at a minimum: 24,000% of Mazda owners would buy another Mazda which is ludicrous.
The rest of the questions I think you answered correctly (I mean you correctly plugged in the corresponding values you got from part 1, the only problem is your part 1 is wrong: garbage in, garbage out).
Recalculate part 1, and if you want, submit them here and I'll tell you if they agree with what I got (before you submit them to your site, I know sometimes these sites take away points every time you submit a wrong answer).
This post was edited by Azrad on May 28 2013 06:20pm