Which property explains why these two expressions are equal?
(w +
2
3
) + 5 = w + (
2
3
+ 5)

Re-written, I believe the equation is:

(W+23)+5=W+(23+5)

With this, the parenthesis have nothing multiplying into it, so we can drop the parenthesis to get:

W+23+5=W+23+5
Which is the same thing.

So I'd assume it is the Associative property, because you are combining the like terms of 23 and 5.

Hope this helps!