Some radicals can be written in a form that they can be either added or subtracted. This new form or simplifying is a method to achieve that.

when we have `(15sqrt6)/(3sqrt3)` it can be written as `15/3*sqrt6/sqrt3`

Now simplify `15/3=5` so we can write our radical as `5sqrt6/sqrt3` or simpler `5sqrt((6/3))`

Then `6/3=2`, therefore you can write it as `5sqrt2`.

1-to simplify `sqrt20` we can write it as:

`sqrt20=sqrt4*sqrt5=2sqrt5`

2-`root3(54)=root3(27*2)`

`root3(27)*root3(2)=3*root3(2)`

3-`sqrt20/sqrt5=(sqrt4*sqrt5)/sqrt5`

`sqrt4*sqrt5/sqrt5` because `sqrt5/sqrt5=1` so we have `sqrt4*1=sqrt4=2`