Question 153544
Remember the expression in the parentheses is a unique expression. 
You can only divide or cancel out terms, inside parentheses, if they match exactly. 
{{{(x^2 - 9)/(x^2 + 3x)}}}
You can factor the top term,
{{{x^2-9=(x+3)(x-3)}}}
and also the bottom one,
{{{x^2+3x=x(x+3)}}}
{{{(x^2 - 9)/(x^2 + 3x)=((x+3)(x-3))/(x(x+3))}}}
{{{(x^2 - 9)/(x^2 + 3x)=(cross(x+3)(x-3))/(x*cross((x+3)))}}}
{{{(x^2 - 9)/(x^2 + 3x)=(x-3)/x}}}