Khan/khan-exercises — pull request #58399 by petercollingridge (2013-08-02 15:59:51+00:00)
Title: Adding and subtracting rational expressions 4

Adding or subtracting two expressions with different denominators, where each is of the form A / (Bx + C).
![adding and subtracting rational expressions 4](https://f.cloud.github.com/assets/219302/902049/8a93cd98-fb8c-11e2-8eb5-5742495b36c2.png)