When you divide a number by a fraction, you should multiply the number by the reciprocal of the fraction. So if you make 1 1/3 an improper fraction you get 4/3. When you multiply 24 by the reciprocal, which is 3/4, you multiply it by the numerator and divide it by the denominator. So
(24 x 3) / 4
72 / 4
18