We are told that one can bake a batch of cupcakes in a fourth of an hour. Since we have to calculate how many batches he can bake in 3 hours, we can calculate the amount of batches we can bake in an hour and then multiply it by 3.
So far, we have the following, every fourth of an hour, we have 1 batch. So, to calculate the amount of batches that we can bake in an hour, we simply divide 1 hour by the amount of time we take to bake 1 batch. That is
[tex]\frac{1\text{ hour}}{\frac{1}{4}\text{ hour}}=4[/tex]So, we can bake 4 batches per hour. That is, in 3 hours we can bake 4*3=12 batches.
In general, to calculate the amount of batches that could be baked in x hours is obtained by taking the total amount of time and divide it by the time that is needed to cook one batch. In this case, we have the following
[tex]\#\text{ of batches = }\frac{x\text{ hours}}{\frac{1}{4}\text{ hour}}[/tex]