Question

Can some one please explain this to me I am completely lost

Answer 1

Let's look at each square root and what we can take out.

$2 \sqrt{20} =2 \sqrt{2*2*5} =4 \sqrt{5}$

3 square root 7 can not be simplified, as well as 2 square root 5.  But, we can change 4 square root 63.

$4 \sqrt{63}=4 \sqrt{3*3*7}=12 \sqrt{7}$

Now, we have:

$4 \sqrt{5}-3 \sqrt{7} -2 \sqrt{5} +12 \sqrt{7}$

We can now complete this problem:

$2 \sqrt{5}+9 \sqrt{7}$

This is the same as the second answer, so that is the correct choice.  Let me know if you need any more help!