Write an expression for m∠ rst

3x – 9

6x – 18

1.5x – 4.5

6x – 9

this is duplicate version of the question i forgot to add a picture to it

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Someone answer this check out the image!

Can someone factor this fully? my friend and i have two different answers and i would like to know if either of them is right. you in advance. a^2 - b^2 + 25 + 10a