We have a proportional relationship like:
[tex]y=k\cdot x[/tex]where k is the constant of proportionality or the unit rate, depending on the context.
If we have a graph, the value of k is the value of the slope.
Knowing one pair (x,y) we can calculate the unit rate k as:
[tex]k=\frac{y}{x}[/tex]In this case, we have one known point that is (6, 2.58), that means that 6 pounds of nails cost $2.58.
We can calculate the unit rate as:
[tex]k=\frac{2.58\$}{6\text{ pounds of nails}}=0.43\$\text{ per pound of nails}[/tex]Answer: the unit rate is $0.43 per pound of nails.