First you need to use two points from store b to find the slope (y1-y2)/(x1-x2). I chose the first two points. (15.54-25.9)/(1.5-2.5)= 10.36. After you take another point from store b to plug into the equation y1-y2=m (x1-x2). M is the slope we just found and I used the first point.
Y1-15.54=10.36 (x1-1.5) distribute the 10.36 to the parentheses.
Y1-15.54=10.36x -15.54 get y1 by itself
Y=10.36x so store b is 10.36 a pound and store a is 7.94 a pound. 10.36-7.94= 2.42
Last one..................................................................................................................................................
