Hey there! :)
We know that 4 bottles cost $2, but we need to know the cost of each individual bottle. We can find out the cost by dividing 2 by 4
.2 ÷ 4 = .5
Therefore, each water bottle costs $0.50! Now that we know the price of a single water bottle, we can simply multiply the amount of students she has with the price of a single water bottle.
24 × $0.50 = $12
Therefore, it costs Miss Smith $12 to buy water bottles for her class.
~Hope I helped! :)