Solve SIR model using Euler's method in C#

Question

The SIR model is:

$$ \begin{aligned} \dot S &= −\beta I S\\ \dot I &= \beta I S − \gamma I \\ \dot R &= \gamma I \end{aligned} $$

I know how to solve SIR with Euler's method in C#. I don't know how to create a suitable class file. Would anyone familiar with C# be able to help please!?