In this case, we have a proportional relationship, since the cost varies directly with the days, this means that as x increases, y increases, and as x decreases, y decreases. A proportional relationship has the form:
y=kx
Where k is the constant of proportionality.
The ratio between them (x and y) is always the same, in this case, the ratio or constant of proportionality is 40, since each day the rent cost increases $40, then:
Constant of proportionality = 40 , replacing 40 for k into the above equation, we get:
equation: y = 40x
We can use this equation to find some pair of values (x,y) to fill the table, like this:
For x equals 2:
y= 40*2 = 80
For x equals 3:
y= 40*3 = 120
For x equals 4:
y=40*4 = 160
For x equals 5:
y=40*5=200
Then, we can fill the table as follows:
We can also use these data to graph the relationship, by taking the point (5,200) and joining it to the origin, we get:
