Adding and subtracting rational expressions 5

Adding and subtracting two expressions with different denominators, where each is of the form (Ax + B) / (Cx + D).

![adding and subtracting rational expressions 5](https://f.cloud.github.com/assets/219302/910327/0d0735ce-fdd8-11e2-9cec-a58cedfb6a9e.png)

This is quite computationally intense (for the student exercise) and I wonder if some answers may cancel in ways I haven't anticipated. The expression editor might be able to deal with this, but I have included data-simplify to avoid people merely typing in the question.