measurement of physiology

A strap, instrumented to measure stretch, is worn around the chest to detect respiration whilst a subject is at-rest. The resulting signal is contaminated by electrical noise from the mains at 50 Hz with a similar amplitude to the respiration signal. Sketch what the contaminated signal might look like.
The signal is then sampled into a computer. Explain what the resulting digitised signal will look like (using sketches if required) if it is sampled at
1. 50 Hz
2. 100Hz
3. 500 Hz
What processing should be done on the computer to recover the respiration signal.