If we take the amount of people we want to serve and put it over the amount the recipe serves we get this
[tex] \frac{18}{24} = \frac{3}{4} [/tex]
We then multiply this times the portion of ingredients the original recipe calls for and get our amount needed to serve only 18 people
[tex]lemon \: lime \: soda \: \\ \frac{3}{4} \times 4 \: liters \: = \frac{12}{4} \: liters = 3 \: liters[/tex]
[tex]sherbet \\ \frac{3}{4} \times 2 \: pints \: = \frac{6}{4} \: pints = \frac{3}{2} \: pints[/tex]
[tex]ice \\ \frac{3}{4} \times 6 \: cups = \frac{18}{4} \: cups = \frac{9}{2} \: cups[/tex]