Hello James!
Graph using the slope and y - intercept.
Slope:

Y-intercept: -3
The graph looks like this ↓↓↓
All you have to do is plug in the number for x, and find y. I will write this out as if in that chart you have shown.
x y = 9 - 3x y
_______________________________________
0 y = 9 - 3(0) 9
1 y = 9 - 3(1) 6
2 y = 9 - 3(2) 3
3 y = 9 - 3(3) 0
Hope that helps!!
5.88 / 3 = 1.96 per pound
original price - 1.21 per pound