There are 720 cans of soup in the supermarket. 350 of the cans on the shelves are vegetarian. 170 of the cans on the shelves are sodium free as well as vegetarian. 40 of all the cans in the supermarket are expired and are not on the shelves. How many cans of soup on the shelves are sodium free?
A. 330
B. 440
C. 500
D. 680