Considering the first sentence, we would note the total cost to be xp.

Going further, the total revenue will be the product of the price and the total amount of corn that got sold. To determine this correctly, the information on locusts must be accounted for. Essentially, while the farmer cultivated x acres, locust reduced the amount of acres he was able to harvest and then sell, so that total revenue is given by q(x-y), where q is the sale price and x-y is the total amount of sold corns.

The gross profit, which is the Total Revenue - Total Cost, is then given by

q(x - y) - xp, which is option A.

Notice how the answer choices also have the trap choice of (x-y)(q-p) in which the information on the locust is not accounted, thus making the choice to be wrong.

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