Answer:
[tex]6\sqrt{2}[/tex]
Step-by-step explanation:
When simplifying surds you need to find a square number that the number is divisible by. In this case root(72) would be divisible by root(36).
This would then turn into [tex]6\sqrt{2}[/tex]. (72 divided 36 is 2 and root(36) is 6)