Supposing that the problem provides the value of circumference of the track, hence, you may find how many meters did she run multiplying 50 by 3 such that:
`3laps = 3*50 = 150` meters
Since the problem requests to use `pi` , hence, you should consider the length of track of `50 m` and you need to use the formula of circumference such that:
`c = 2*pi*r => c = pi*D = 50*pi`
Hence, one track represents `50*pi` meters and you may find how many meters she run such that:
`3*c = 3*50*pi =150 pi ` meters
Hence, evaluating how many meters Hilary covered after 3 laps, considering the length of track of 50 m, yields `3*c = 150 pi ` meters.