Calculate the cost per banana for Sam's purchase: $2.10 divided by 7 bananas equals 0.30 per banana
Then Calculate the cost per banana for Diane's purchase: $1.20 divided by 4 bananas also equals 0.30 per banana.
Since the cost per banana is the same for both Sam and Diane, the constant of proportionality is $0.30
=$0.30 per banana.
