c# - showing a form from one project in another

I need a example of the following First lets say we have Project A and Project B Now in project A the form is called frmMain and project B is called projB Now I know how to show the projB from the project A but what I need to do is click a button on the projB (projectB) and show the frmMain from ProjectA I just need a sample project so I can mimic to the actual project I am doing. I will like as well for you to write how to do it in a document in case I miss something when I look at the sample. This is a project I would like to Hire and do it within the next hour