The answer is A because you need to find the unit rate of each cost
Since $2.80 is for 2 liters, do 2.80/2 which equals 1.4. So that’s the cost for one liter
Then, 6 half liter bottles is just 3 liters because 6*1/2= 3. Then to find the unit rate for that, do 3.90/3 which equals 1.3.
So the first option is $1.40 per liter and the second option is $1.30 per liter so the first option is more expensive- the 2-liter bottle, and the cost for that is 1.40
Hope this helps:))