Economists use the word marginal to mean an extra or additional benefit or cost of a decision. an optimal decision occurs when
a. marginal cost is zero.
b. marginal benefit is greater than marginal cost.
c. marginal benefit is maximized.
d. marginal benefit equals marginal cost.

Option D

Explanation: In simple words, optimal decision refers to the decision that results in at least that level of utility benefit as all other available options do . In other words, it has maximum potential for profit and least expectation of loss.

In such decision the utility is taken into consideration and is calculated on the basis of marginal cost and marginal benefit. If it provides for the higher probability that the marginal cost will be equal to marginal benefit than it would be considered as an optimal decision.

Hence the correct option is D.

$43,000

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.2*215,000 = 43,000