It is like putting a mirror on the y-axis. It is asking what point is the photo negative of the point, like a mirror. You see yourself in the mirror but everything is opposite. Your right hand is your left. So which point is the photo negative of (3, 7)? (-3, 7) Because it is only across the y-axis, the y value stays the same.
<em>b</em><em> </em>for <em>books</em><em> </em>read. b=1x + 1. the amount of months he's been in the club goes for x and +1 because he already read a book before he joined. if you do easy math, he's been there for 8 months because he read 9 books. i probably got the equation backwards but this works both ways imo.