Question 68801
Well if you're looking to simplify the expression you should find the perfect squares that are also factors of 120. The only perfect square that will work is 4, so {{{-3*sqrt(120)}}} can be written as {{{-3*sqrt(4*30)}}}. 
Since a square root of a product is a product of square roots, (ie. {{{sqrt(xy)=sqrt(x)*sqrt(y)}}}), the expression then becomes {{{-3*sqrt(4)*sqrt(30)}}}

Since 4 is a perfect square, the square root is 2, the expression becomes


{{{-3*2*sqrt(30)}}}. 

Further simplication leaves the answer

{{{-6*sqrt(30)}}}.