How do you simplify 4 square root of 27 – square root of 75?

First get some squares out from under the root

##27=3^2*3->sqrt27=sqrt(3^2)*sqrt3=3sqrt3##

##75=5^2*3->sqrt75=sqrt(5^2)*sqrt3=5sqrt3##

Answer:

##4sqrt27-sqrt75=4*3sqrt3-5sqrt3=7sqrt3##