A model of 9/12 will have 12 parts, 9 of which are shaded.
A model of 3/4 will have 4 parts (1/3 as many), 3 of which are shaded. Each part of this model will correspond to 3 parts of the 9/12 model. Hence, each part is 3 times the size of a part in the 9/12 model.
