Answer:
B.
First you find the square root of 72 but it has none so instead you find the what multiplies to 72 but is still a perfect square. That is 9 times 8. The square root of nine is 3 so we leave that outside of the radical, and leave the 8 in there. Then we go to x. Exponents follow a different rule and you cannot get the square root of them so find if it's divisible by 2 by taking away 1 from nine making it x^8 and x. Then divide the 8 by 2 and you get x^4, leave the remaining single x in the radical. Bring that behind the 3 on the outside and do the same with the y. Now the y can be divided by 2 so that will be 8. Now there should b 3x^4y^8(radical sign)8x