Hi there! Thank you for the opportunity to help you with your question!

When we have sums such as

3x^2y - 9x

We can always look for things that all terms have in common. The first thing to notice, is that both terms are divisable by 3. Therefore, I can "factor out" a three from both terms. This is the "inverse" of the distributive property:

3*(x^2y -3x)

[If you multiplied the 3 back in, you would go back to the original expression.]

Now, note that the two terms still have something in common, an "x". I can similarly factor it out:

3*x*(xy - 3)

And this is the factored out expression.

Please let me know if you need any clarification. Always glad to help!