How can you recognize a linear equation

Which representation has a constant of variation of -2.5

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?

What is the 17th term in the arithmetic sequence in which a6 is 101 and a9 is 83