Thank you for the opportunity to help you with your question!

You have to work your way from the bottom fraction to the top fraction :)

The answer is:

2a(5a-7)/(7a-10)

Please let me know if you need any clarification. I'm always happy to answer your questions.

Oct 14th, 2015

Because this is an easy question, we only have 20 minutes to answer. I am now going to type up the "how" of how this is done, because while the problem is easy, it's very difficulty to format in only 20 minutes :)