Two numbers are 10 units away in different directions from their midpoint, m, on a number line. The product of the numbers is –99.

The numbers are 10 units on opposite sides of their midpoint, so they are m − 10 and m + 10. Their product is −99, giving (m − 10)(m + 10) = −99. Using the difference-of-squares rule, this becomes m² − 100 = −99, which is choice D.

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