It's a math rule that we must solve first what's into a brake or parenthesis, so,
First: Product of powers
According to the exponent's law, we have a product of powers case, so, we need to sum the exponents and keep the base
Exponents: 5 and 3
Base: 7
Applying it we have:
Then,
We have a power of a power case, which involves multiplying the exponents:
Exponents: 3 and -4
Then,
Finally, we can apply the negative exponents, the negative exponent's rules state that negative exponents are the reciprocal of the positive exponents,
It's a rational number. 9 is a perfect square. What you have asked is written as -sqrt(9), which can be written as -sqrt(3*3) which is - 3. That's perfectly OK. What would not be OK is something like -sqrt(10) which is irrational because it cannot be represented as a fraction or a whole number or a repeating decimal or a decimal that terminates.