In noisy factory environments, it's possible to use a loudspeaker to cancel persistent low-frequency machine noise at the position of one worker. The details of practical systems are complex, but we can present a simple example that gives you the idea. Suppose a machine $5.0 \mathrm{m}$ away from a worker emits a persistent $80 \mathrm{Hz}$ hum. To cancel the sound at the worker's location with a speaker that exactly duplicates the machine's hum, how far from the worker should the speaker be placed? Assume a sound speed of $340 \mathrm{m} / \mathrm{s}$.