The cost of a candle varies directly with the volume of the candle. If a candle with a volume of 80cm^3 costs $12, what would be the cost of a candle with a volume of 120 cm^3?

First, you need to find out how much will the candle cost per volume. If a candle with a volume of 80cm^3 costs $12, the price of the candle per cm^3 would be: $12/80cm^3 = $0.15/cm^3

Then the price of a candle with 120 cm^3 volume would be:120cm^3 * $0.15/cm^3 = $18