Explanation

This problem defines a function for the made-up symbol #.

In this problem a = (–4) and b = 4.

Plug the values into the function: \((-4)^2 \sqrt{4}- (-4) = 16 \times 2 + 4 = 36\).

Do not forget to keep the parentheses around the –4!

Also note that only the positive root of 4 applies, because the problem has been presented in the form of a real number underneath the square root sign.
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Updated the question
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----why -28 is not answer?

It is just a matter of substitution

a=-4 and b=4

\(a^2 \sqrt{b} - a\)

\(-4^2 \sqrt{4} - (-4)
\)

\(16 \times 2+4=36
\)

Regards
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