Answer:
Pat a) The unit rate of graph at left is

Part b) The unit rate of graph at right is

see the attached figure
Explanation:
we know that
The unit rate of a linear equation is the same that the slope of the linear equation
step 1
Find the slope of the graph at left
This graph represent a proportional relationship (because the line passes through the origin)
The slope is equal to the constant of proportionality k

we have the point (1,25)
substitute the values in the formula

step 2
Find the slope of the graph at right
we have the points (2,80) and (3,120)
This graph represent a proportional relationship (because the line passes through the origin)
The slope is equal to the constant of proportionality k

Is necessary only one point to determine the constant of proportionality
take the point (2,80)
substitute the values

Verify
The formula to calculate the slope between two points is equal to

we have the points (2,80) and (3,120)
substitute the values

