So the bottle of water costs $1.75. The total was $9.25. To find how much the 3 boxes of popcorn cost, you have to do the cost of the bottle of water from the total. ($9.25 - $1.75 = $7.5) Now what we have to do is find the cost of 1 box, we know that 3 boxes is $7.5, so then we need to do $7.5/3 ($7.5 ÷ 3) 7.5 divided by 3 is 2.5. Therfore 1 box of popcorn is $2.5.
