These are the ingredients needed to make 18 rock cakes
9 ounces of flour
6 ounces of margarine
2 large eggs
6 ounces of sugar
8 ounces of fruit
how much of each ingredients will you need to make 12

First we divide all of the ingredients by 18 to see how much we nee for one rock cake.

9 / 18 = 0.5
6 / 18 = 0.33
2 / 18 = 0.11
6 / 18 = 0.33
8 / 18 = 0.44

Now we multiply all of these by 12.

0.5 * 12 = 6 ounces of flour
0.33 * 12 = 3.96 ounces of margarine
0.11 * 12 = 1.32 large eggs
0.33 * 12 = 3.96 ounces of sugar
0.44 * 12 = 5.28 ounces of fruit