To answer this question you will need to know how many quarts there are in one gallon (the conversion of 1 gallon = 4 quarts). This is 15 3/4 groups of 1 gallon which is the same as 15 3/4 groups of 4 quarts.
15 3/4 x 4 - convert the 15 3/4 and 4 to improper fractions.
73/4 x 4/1 (you can cross cancel the 4's because one is in the numerator and one in the denominator (4/4=1),
73/1 = 73 quarts in 15 3/4 gallons.
Mrs. Martin made 73 quarts of sweet tea.