You can obtain an explanation for any step by clicking on it. Please note that you cannot click on the very first expression, which is the original problem. 

In short, in Step 3 we pull 'x' in front of the brackets for the first two terms and '3' in front of the brackets for the second two terms:

x^2 + 2x + 3x + 6 = x(x + 2) + 3(x+2)

While in Step 6, we pull '(x+2') in front of the brackets:

x(x+2) + 3(x+2) = (x+2)(x + 3)

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