Explanation:
cost to produce 120 units
= C(120) = 1000+5.7(120) + .7(120^2) =
= 11764
cost to produce 100 units = C(100)
= 8570
rate of change = (11764-8570)/(120-100)
= 3194/20
= 159.70 dollars/unit
repeat the process for 100 to 101
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