@Carl Love 

The goal is to find an expression for each variable as a function of the time t, for example:

P_Al_b = C1*exp(C2*t) with C2,C2 constants

The expressions are needed for plotting. If this can be achieved by solving the equations numerically, could you point me in the direction of how to do that? :-)

Thank you in advance!

@Carl Love Many, many thanks for your reply!

I had been looking at the int/details help page and tried a few of those methods, but didn't know the Evalf(Int()) methods also apply to int(). I'm glad it works and that the solution was that simple (and fast!).

However, could you help me understand a couple things?

1. From what I understand from the int and evalf/Int help pages, wouldn't it be more correct for me to use evalf(Int()) instead of int()? 

2. I tried using the method _d01akc instead of _d01ajc to see if it would yield the same result (and it did). From the description of the two methods I expected them to give the same result, but what is the actual difference between those two methods? Does it matter if I use one or the other for my purpose?

These questions are just out of curiosity, to help me understand why and how the problem is solved :-) 

Once again, thank you so much for your help!