We have to find out which option has the higher cost per liter. To do this we must find out how much each option would be if it was a liter.
1st set up each equation 2-liter = $2.80 we can divide by 2 on both sides of the equal sign and we get 1 liter = $1.40. 6(1/2) liter bottles = $3.90 this becomes 3 liters = $3.90 then we divide by 3 on both sides of the equal sign and we get $1.30