can anybody help me please?

I would like to be able to link to other solutions.
For example -
I may keep all my comment routines in a project called-"common routines"
it is possible for me to add the necessary files to projects. However, as time goes on and I working on projects I may create new seven routines which I want to include in future projects.

If I simply add the files to the project, I will have is to modify the "common routines" each time I make a change to keep the files up to date.

What I would like to do is to make the change in the "common routines"solution and have these available to all projects, without having to add the files again, is there any way of doing this?

Thanks for your time reading this.