Aiko is finding the sum (4 + 5i) + (–3 + 7i). She rewrites the sum as (–3 + 7)i + (4 + 5)i. Which statement explains the error Aiko made by using a mathematical property incorrectly?

Aiko changed 4 + 5i into (4 + 5)i, and –3 + 7i into (–3 + 7)i. That incorrectly treats the real numbers 4 and –3 as coefficients of i; the distributive property does not justify that change. The correct sum combines real parts and imaginary parts separately: (4 – 3) + (5 + 7)i = 1 + 12i. The statement that she misused the distributive property is choice D.

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