Will award ! why do stars cluster together to form galaxies? why do galaxies cluster with other galaxies? i think it's gravity but i'm not sure. (also i put mathematics cause there is no science option)

They can be thrown into new orbits, or even thrown clear of their parent galaxies into intergalactic space. While galactic collisions rarely destroy stars, they often create them. As vast clouds of gas and dust in merging galaxies slam together, they can create thousands or even millions of new stars.

-Galaxy Formation | StarDate Online

https://stardate.org/astro-guide/galaxy-formation

it's d.

step-by-step explanation:

because: -1(4x + 1y) +2 (1x-3y) distribute each number into the parenthesis.

then you would get: -4x - 1y + 2x -6y combine like terms

and get: 2x -7y

hope my answer has you if not then i'm sorry.