Which of the following illustrates the commutative property of addition?

6 + 3 = 3 + 6
9 + 0 = 9
3(10 + 7) = 3 × 10 + 3 × 7
(11 + 2) + 8 = 11 + (2 + 8)

Barney & noblet customers can choose to purchase a membership for $25 per year members receive 10% off all store purchases 1. how much would a member pay per year if he bought $50 worth of items each year? 2. write a slope-intercept equation that expresses how much a member pays per year using x to represent his purchases per year 3. how much would a member have to spend per year to pay off his membership fee?