Elli says 3 + (x + 1) is equivalent to (3 + x) + 1. Gabe says 3 + (x + 1) is equivalent to 3+ (1 + x).
Who is correct and what property did they use?

What number is 7 units left of -15?

The collection of beautiful oil paintings currently on display at an art gallery well defined; set not well defined; not a set

The table below shows the number of free throw shots attempted and the number of shots made for the five starting players on the basketball team during practice. each player's goal is to make 80% of her shots.