Mono how to get variable in C++ from C#?

Question

Mono

I have a C# library with the following code:

public class Eng
{
      public Vector3 pos;
}
public class Vector3
{
      public float x;
      public float y;
      public float z;
}

How to get the class that is in the pos variable through mono in C++ and then get the x value from the Vector3 class?