Answer:
d) He divided the exponents in the parentheses instead of subtracting
Explanation:
First you should know that the power of a power based
"a" is the power based on "a" and whose exponent is the product of the exponents:

By simplifying the expression you get,

What Blake did wrong is what says option d) He divided the exponents in the parentheses instead of subtracting.
This is what he did wrong:

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Hope this helps!