Can you define galaxy(don't forget to use the word gravity in your answer)?

A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

hope this helps (:

The purpose of a lab is to do your "expirements" the importance of the topic is so you can now what the story is about and the last one is because no one is me with my question ( what is 3 over 4 x - 9 = 27 maybe you can )