[Tricxta]

You're asking how many times 2 goes into 100? lol
Anyhow if it's not and I mis-interpreted the question and the length of a car is 2 units as well as the width... then I'd:
1)Find the original radius:
100=2*pi*r
100/2/pi=r
r=15.9(rounded)

2)then subtract 2 units(length of the car) from that
r=13.9

3)Find the new circumfrence
circ=2*pi*13.9
circ=87.3(rounded)

The amount of cars able to fit in the parking lot is now:
=86/2
=43