They are asking you to find the square root of the letters. When you have the square root of 9, the answer is 3 because 3x3 equals 9. So we do the same thing with this problem.
Sorry, I don't have any of the math symbols on my keyboard.
When you have the square root of a^3b^4, you pull out anything that can be multiplied by itself.
a*a= a^2 we can pull out a^2, but we will have an a left under the square root symbol.
b^2*b^2= b^4 we can pull out a b^2 and we will not have any left under the square root symbol.
So the answer is the 3rd down: ab^2(a)
I used the parentheses for the square root symbol.
I hope this makes some sense for you! Good luck! :)