AGILE 

I finished the task but have some comments....

I did a basic scaffold for charges so I didn't add scaffold for card and fee_details
If you want to add a scaffold for card, we can add its fields in the same charges table or in a separate table and make 1-1 association
If you want to add fee_details, it will be 1-M association

Actually, I recommend cucumber over rspec for functional and behavior tests and recommend specs for model testing
We can also use factories instead of seeds to prepare tests data.

As I mentioned on my message when I accepted the job, I am a RoR team lead, I manage a team of 5 RoR developers.
I can assign you a senior RoR developer https://www.odesk.com/users/Software-Developer_~~5a165303c0540661?sid=49002&tot=12&pos=3
He can work ~15hrs/week. I can also work with him 5-10hrs/week. We will be available to start your job 26Aug because we are in a feast vacation starting from next Sunday for one week.

I can assign you also a junior RoR developer starting from 16 Sept. He can be available as a full-timer if you wish.

Thanks for contacting me and hope we work together in the future...