Question 832035
Well you get {{{3x(x+3) = 0}}} and that's right, now only the "set factors to 0" confuses you right?
Factors are those terms that multiply together, and for solving equation, They mean "factor" are those terms that multiply together but those terms must involve an unknown variable, like x, y, z, a, b, c, etc 
Let's talk about the problem
Let's talk about the right side
3x(x+3) 
What are the terms that multiply together in this side? 
They are 3, x, and x+3 right? Since you have 3 times x times (x+3) give you 3x(x+3)
So you have 3 factors, but remember, in solving equation, we only take factors that involve unknown variable, that means we throw the 3 away, we only take x and x+3 
Now let's "set each factor equal 0" 
{{{3x(x+3) = 0}}}
{{{x = 0}}} and {{{x+3=0}}}
{{{x = 0}}} and {{{x = -3}}}
So your solutions are 0 and -3 
TA-DAH
:D