For Loop

Hey Guys,

So, i'm trying to do For loop in my file to define a concentration changes in respect to x.

The approach used : 

I have to first solve the CO2lSS with ode solver and resulted in CO2lSS(x).

And from there i substitute into the equation of CO2gSS(x) equation, where inside the equation there the CO2gin and CO2lin which i want to do iteration.

CO2lin (n) has to equal to the CO2lout (n-1) and CO2gin (n) has to equal to CO2gout (n-1).

Where n is the number of cycle, and each cycle is 250 m.

So i want to make a loop where everytime the concentration reach x=250 m, that value will be used for another concentration in value.

I tried but it still gives error. Hope you guys can help.

I would really appreciate it.

Thank you.