Identify whether or not the expressions are equivalent and name the property that makes them equivalent(12 + 15) + 20 = 12 +(15 + 20)

At a sale this week, a desk is being sold for $213. this is a 29% discount from the original price. what is the original price?

The sat and act tests use very different grading scales. the sat math scores follow a normal distribution with mean 518 and standard deviation of 118. the act math scores follow a normal distribution with mean 20.7 and standard deviation of 5. suppose regan scores a 754 on the math portion of the sat. how much would her sister veronica need to score on the math portion of the act to meet or beat regan's score?

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?