we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form
y=kx
where
k is the constant of proportionality
Find the value of k for each customer
If the value of k is the same , then the relationship is proportional
step 1
Find the value of k customer 1
y=kx
k=y/x
y=4.50
x=1.5
substitute
k=4.5/1.5
k=3
step 2
customer 2
y=12
x=4
k=12/4=3
step 3
customer 3
y=16.50
x=5.5
k=16.5/5.5
k=3
therefore
the scenario is proportional
If the scenario is pproportional, then the ratio between the price and the pounds must be constant
If the ratio is not a constant between the price and the pounds, then is not a proportional
Example
if the price is $10 for 5 pounds of bananas
the value of k=10/5
k=2
In this case the values of k are not equal
k=3
k=3
k=3
k=2