Step 1
Let
x------> the cost in dollar
y-----> the pounds of grapes

we know that
A relationship between two variables, x, and y, represent a direct variation if it can be expressed in the form
or 
The line in the graph represent a direct variation
Find the constant of proportionality k
------> substitute point B -----> 
The slope is equal to the constant of proportionality
so

the linear equation is 
therefore
<u>the answer Part a) is</u>
For every dollar you spend, you can get
pounds
Step 2
Find the cost for one pound of grapes
Let

substitute the value of g in the linear equation and solve for c



therefore
<u>the answer Part b) is</u>
For each pound of grapes, you would need 