combining schedules

[jk.127024]

We have a project in which one schedule(Residential Floor Areas) contains the area of the residential build out per floor and another schedule(Mechanical Deductions) which contains the area of mechanical deductions per floor. Does anyone know how to join the Mechanical Deduction schedule to the Residential Floor Areas schedule so that we can then add a new parameter(in the RFA sched) which subtracts the deductions from the floor area. I am new to Revit but this seem like common database functionality so I assume it can be done. Any help would be greatly appreciated.
Thanks
Jon