a manufacturer can produce tape recorders at a cost of $20 apiece. It is estimated that if the tape recorders are sold for x dollars apiece, consumers will buy 120-x of them each month. Use calculus to determine the proce at which the manufacturer's profit will be the greatest.
I set up the problem like this (please double check this)
R=2400x - 20x^2
R'(x) = 2400-40x
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