First, note that sqrt(27x^4)=sqrt(27)*sqrt(x^4)√27x4=√27⋅√x4. Next, since 27=9*3=3^2*327=9⋅3=32⋅3, we can say sqrt(27)=sqrt(9*3)=sqrt(9)*sqrt(3)=3*sqrt(3)√27=√9⋅3=√9⋅√3=3⋅√3.
Also, sqrt(x^4)=sqrt((x^2)^2)=x^2√x4=√(x2)2=x2 (in general, sqrt(y^2)=|y|√y2=|y|, but if y=x^2y=x2, then y\geq 0y≥0 anyway so we can get rid of the absolute value sign).