Homework question about alice in wonderland?

In chapter 2, "The Pool of Tears", Alice tries to perform multiplication but produces some odd results: "Let me see: four times five is twelve, and four times six is thirteen, and four times seven is—oh dear! I shall never get to twenty at that rate!" This explores the representation of numbers using different bases and positional numeral systems (4 x 5 = 12 in base 18 notation; 4 x 6 = 13 in base 21 notation. 4 x 7 could be 14 in base 24 notation, following the sequence).