The answer should be C if the problem is correctly was properly written.
We start out with (3x^-4)^2 * (5x^-2) which we can simplify.
We do (3x^-4)^2 first and simplify it by squaring the number and term which gives us 9x^-8 which is then multiplied by the rest of the equation, (5x^-2).
This gives us:
(9x^-8)(5x^-2) = 45x^-10 or 45/x^10 which is C.
We multiply the numbers and add the exponents to get 45x^-10 and we know that to make the exponent positive, we move it down to the denominator so it becomes 45 / x^10.
I hope you get it now. :)