The number in a radical needs to be square rooted to get placed out of it, so the square root of 20 can be split into the square root of 4 times the square root of 5, which can then be simplified to 2 rad 5, but there is a 2 outside of the radical, so then it becomes 4 rad 5, which is equivalent to 4 rad 5 so the first one is an answer.
Raising a number to the exponent of 1/2 is basically square rooting it.
For the second one, it's rad 6 - rad 5, which is not equal to 4 rad 5. That is not an answer.
For the third one, it's 3 times rad 5 + rad 5. That's 3rad5 + rad5. That's 4 rad 5, which is equal to 4 rad 5 at the top, so this is an answer.
For the fourth one, it's 4 times rad 5, so that's 4 rad 5, which is equal to 4 rad 5. That is an answer.
For the fifth one, 10 cannot be simplified to get out of the radical because it's only factors are 2 and 5, and neither of them are squares. That is not an answer.
For the sixth one, it's 3 times rad 5, so it's 3 rad 5. That is not an answer.
The answers are the first one, third one, and fourth one.
Hope this helps
