how to define url path to access child projects from main project

I have 3 projects- Main Project, Project A and Project B. I have added reference to both A & B inside Main project. Now, if i make ajax call from Main project to say Project A (web service project), how would my url look like? I have tried using localhost, but i ran into CORS issue. So, is there any solution for that? thnks.

var url = '../ProjectA/someService.asmx?op=Action';