The last answer is correct.
First you divide 128 by 2 and get 64
The square root of 64 is 8 which means you bring out an 8, this eliminated the first 2 answers.
Then you use the reciprocal strategy to cancel the exponential values and get xsquared on the bottom and y to the first power on the top. since xsquared can be square rooted, it is no longer under the root, which just leaves Y.
