How to solve this problem by rationalizing the denominator? Steps please.

4sqrt6/sqrt30

since the bottom is just √30, multiply top and bottom by √30. You then have

(4√6 √30)/(√30 √30)
= 4√180/30
= 24√5/30
= 4√5/5

or, you could note that
√6/√30 = √(1/5) = √5/5