Question: plotting

This is my problem:
i've an nonlinear system of six equations and i find the
solution with Runge-Kutta:

for every t>0 i've
x[1](t), x[2](t), x[3](t), xc[1](t), xc[2](t), xc[3](t).

I write this solution in the vector "solution"

> solution:=dsolve(...

Yet i've also another equation ("EQ7") of the type:

EQ7 = f(xc[1](t),xc[2](t),xc[3]) with xc[1],xc[2],xc[3] presents in "solution".

I desire the graph of

EQ7 = f(t)

I've write this:


> time:=150000
> for qtime from 0 to time by 150 do
     x(qtime):=qtime:
     FF(qtime):=evalf(subs(
                           xc[1](t)=rhs(solution(qtime)[5]),
                           xc[2](t)=rhs(solution(qtime)[6]),       
                           xc[3](t)=rhs(solution(qtime)[7]),
                                                      EQ7)):
  od:


> PL80:=plot({seq([x(qtime),FF(qtime)],
  qtime=0..tempo)}):
  display(
  PL80,
  axes = normal,
  labels=[secs, Fj(m^3/s)],
  title = `without saturation`,
  view=-1..0.1);



but this "for" cycle in many onerous. Have you another solution?