To state what fraction of 1 quart is 3 cups, you must use the fact that 1 quart is 4 cups. This means that the total unit, 1 quart, is equivalent to 4 cups. Then, you use 4 cups as the total unitl or the denominator of the fraction, and 3 is the numeratior = 3/4. Also you can think that you need 3 cups out of 4 cups is 3/4.
