Hello!

I have a system of equations that I dont know how to solve. I want to know what is the value of X1 and X2 at a specific point. I have a system of equations that follow this:

if t is between 0 and 1:
X1 varies according to the function Xtot-(kp X8 A-k4 X3[t])
X2 varies according to the function kp X8 A-k2 X2[t]

if t is between 1 and 60:
X1 varies according to the fucntion -k4 X3[t]
X2 varies according to the function -k2 X2[t]

Constants through time: Xtot, kp, X8, A, k2, k4.
through all time we have X3[t]=Xtot-X1-X2.

my problem now is, i want to compute the values of X1 and X2 at t=60, but these values depend on the values that they have at t=1. I know this is a simple question, but I dont know how to do it... This is all the information that I have. Could you please give me some tips on how to solve this?

thanks