How to solve two differential equations

I wrote this to solve two differential equations but does'nt work

clc
clear
syms B(t) S(t)
K=0.000001;
k=0.3;
DB=diff(B);
DS=diff(S);
eq1=DB==k*B*S/(K+DS);
eq2=DS==-0.75*k*B*S/(K+S);
cond=[S(0)==5,B(0)==0.05];
[B,S]=dsolve([eq1,eq2],cond)

[Torsten]

I doubt there is an analytical solution for your system because of the S and DS-terms in the denominators.

Use one of the numerical integrators instead, e.g. ODE45, ODE15S.