Process Modeling nonlinera optimization

How do I plot V against r for the following equations.

dX/dt = rX; dQ/dt = m*X dV/dt = -n

if v >0; r= (0.5*V/(0.4+V))*(1-X/30)(1-Q/170); m = 3.5*r+.12; n= X(r+.2);

t= [0 10]; Q=[0,50]; V=[0,50]; X=[0,30];

else r = 0;