Blake's mistake is (d) He divided the exponents in the parentheses instead of subtracting.
<h3>How to determine the mistake</h3>
The expression is given as:

The actual solution is as follows:

Add the exponents

Multiply 15 by 5

Blake's simplified expression showed that:
He divided 12 by -3 and then multiplied the result by 5
Hence, Blake's mistake is (d) He divided the exponents in the parentheses instead of subtracting.
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brainly.com/question/4344214