Yinka you're defining quite a complex system all at once.

I imagine you've a desired output, perhaps you want to see one or two variables in terms of the others. Taking so many steps simultaneously, its unlikely you'll get anything close to useful. When the computation finishes I'd expect a far more complicated output than your input!

Define just the one or two relationships and solve that simple system. This will let you observe the breadth of the solution and prune it a bit. For example, you may find the solutions deal rigorously with complex numbers, which might be superfluous for your system, you can then solve again assuming that said inputs are reals or integers.

Whilst Mathematica is a heavy tool, unless you apply it very gently you will only magnify your problem. The very first condition of your system is r-RF==0, why force your computer to play with unnecessary variables!?

A final note on legibility, the Greek alphabet is readily available in Mathematica, just press escape, the most probable letter, and escape again. Eradicating your "SIGMA"s et cetera will make things easier to look at and to understand.