Create a function as ODEs solution

I try to create a user function as a ODEs solution for this task

http://communities.ptc.com/message/223872

I do not know how to do it with the odesolve function but I know how do it with the rkfixed function. But I do not remember how use rkfixed for this ODEs.

Help me please - the Mathcad Prime 3 sheet in attach.