Every month, Midtown Grocery Store donates 8-ounce cans of vegetables to a food bank. The food bank's volunteers fill bags with these cans and deliver the bags to families in need. There is a proportional relationship between the number of bags the food bank's volunteers can fill, x, and the total number of cans they deliver, y.
x (bags) y (cans)
5 45
6 54
8 72
11 99
What is the constant of proportionality? Write your answer as a whole number or decimal.