1. It seems rather trivial, but make sure project A is compiled and archived before project B is archived.
You can do this by setting project dependencies by right clicking any of the projects A and selecting Project Dependincies.
2. Not sure if environment variables in VS are case sensitive, but it is usually spelt
$(SolutionDir)
3. Make sure that A.lib exists in the specified folder, and you have spelt its name correctly.