Analytical problem is simple but I am not sure is it possible in this kind of system. I will give my idea. We can apply on first equation d/dx and then that it is possible to substitute from second equation dQ/dx in first, but the problem is that we have Q on two places and coefficient in front is not the same (A and B). A, B, C, D , E and F are constants.
Equations are here:
http://www.2shared.com/photo/HBJIhJQX/Clip.html