Why? I asked...

Also I am pretty sure in the future, maybe not my future, there will be a way to travel through time.
Riddle me this:
You're in a car travelling at 100mph
On the front of your car is a gun pointing forwards..
On the back of your car is a gun pointing backwards..
The guns both shoot their bullets out at 100mph when fired.
Ok..so you're travelling at 100mph, so are the guns attached to your car..
you fire both guns *bang*, one in front, one behind, both bullets are forced out at 100mph.. simple enough?
1(a)
How fast would you measure the bullet in front to be travelling away from you?
(b)
How fast would you measure the bullet behind to now be travelling away from you?
An idle bystander is also taking measurements of the bullets speeds from the sideline..
2(a)
At what speed does he measure the bullet which was shot forwards to be travelling through the air?
(b)
& at what speed does he measure the bullet which was shot behind you to be travelling through the air?