Denny uses 81 gallons of water to wash 12 dogs. If the amount of water used varies directly with the number of dogs washed, how many gallons of water will be needed to wash 42 dogs? Assume that the number of dogs washed is the independent variable.

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.