Use the properties you learned to show why (a+b)+c is equivalent to b+(a+c)

Using the Associative Property of addition, if you move the parentheses anywhere between a, b, and c, the answer will always be the same. Also, the Commutative Property of addition states that if you move the terms around, the answer is also still the same. So, (a+b)+c is the same as b+(a+c). 

What's the denominator

Ithink it’s b because it say 3 plastic rings and all the balls