They said 4x to the power of NEGATIVE 1/2.
That would be 1 divided by root 4x, and if you multiply that by root x, it's root x over root 4x. Since you can't have a radical in the denominator, multiply the top and bottom by root 4x. So then it's root 4x^2 (because when you multiply radicals you multiply the numbers underneath) over 4x. And the square root of 4x^2 is 2x, so you get 2x over 4x. And THAT can be simplified into x over 2x, or basically 1/2.
So your answer is 1/2.