Question 1172067
Set it up as an ordered pair
(2, 4.50)
(4, 9)
(10, 22.50)
The slope is 4.50/2 or 2.25
slope-intercept form is y-y1=m(x-x1), m slope, (x1, y1) a point
so y-9=2.25(x-4)
y=2.25x
no constant. 
each pound of grape is $2.25.
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Can also be done by inspection. 10 pounds-22.50 is $2.25 per pound.
2 pounds for $4.50 is the same.