Anyway, I understand what you mean because we constructed a few of those ovals before.
The inside track:
(Assumed to be the innermost of the oval for this exercise)
Perimmeter, P1 = 400m
P1 = (two semicircles) +2(90) = 400
two semicircles = 400 -180 = 220
one circle = 220 m in circumference
radius, r = 220 / 2pi = 110/pi meters.
The outdside track:
(assumed also to be the outermost of the oval for this exercise.)
radius, R = r +8 = (110/pi0 +8
Perimeter, P2 = (two semicircles) +2(90)
P2 = one circle +180
P2 = 2pi[(110/pi) +8] +180
P2 = 220 +16pi +180
P2 = 400 +16pi meters
So, P2 -P1 = (400 +16pi) -400 = 16pi
Meaning, it takes 16pi meters more to run around the outside track.
In decimals, that is 50.27 meters more.