Obviously if we accept the formula and we add velocity of one car going in one direction at 60 mph with the other car also going 60 mph in the opposite direction we get 120 mph. My problem isn't math it's that the actual 60 mph is in relation to what is not moving which is the earth or ground beneath each car. The 120 mph removes the immovable ground but by doing that we have no bases for the 60 mph that 120 mph depends on.
I hope you get my point. Without "that which does not move" I can't get a speed/velocity for either car
Incorrect. You have a reference point that, relative to itself, is not moving. You don't need the ground to measure distance, just a way to measure distance.
so I have no numbers to add up in order to get a velocity for a relative speed of two cars/things.
SURE YOU DO! you have one car as your reference point, and the other car moving at 120 mph away from it. The ground has nothing to do with the relative velocities of two cars.
All reference points must be "fixed" and that means "immovable".
They ARE immovable, relative to themselves!
To the driver of one of the cars moving at 60mph relative to the earth, the earth is the object that's moving at 60 mph, while the car is stationary.
To an observer watching the car standing on the ground, the earth is motionless while the car moves.
If it were (and it's not) possible to stand on the poles of the sun, an observer at either would see the earth orbit the sun once every 365 days, while the sun wouldn't move.
Motion is relative, Dave.
The one observing, or the reference point he uses, is always considered motionless, even though it is moving.