Question 287292
actually you have to simplify first
sqrt(27)-5sqrt(12)
sqrt(27)=sqrt(3*3*3)=3sqrt(3)
sqrt(12(=sqrt(2*2*3)=2sqrt(3)
so we have 
3sqrt(3)-5*(2sqrt(3)
3sqrt(3)-10sqrt(3)
(3-10)*sqrt(3)
-7sqrt(3)