Jennelle buys 32oz for $2.56, that means 32/2.56 = 12.5oz per dollar
Amina buys 6oz for $0.48, that means 6/0.48 = 12.5oz per dollar
So the answer is:
Yes, it is proportional because they received the same amount of yogurt per dollar
If y is the cost in dollars, and x the amount of yogurt:
we just found tha the quantity of yogurt per dollar is 12.5
therefore: y/x = 12.5
solving for y (cost):
y = 12.5 x