resolution stuck system polynomials order two

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I have three variables (ISP, ch, $n_C$). I have two equations. My aim is to solve a system of two equations to compute the values of ISP and ch according to $n_C$.

My two equations are polynomials of order two. I put the equations in a framabin : https://framabin.org/p/?2ea1412d13d7f...

I tried the solvers of sage and simpy but it does not work. I tried to use Groebner basis but I failed.