A observation is gathering data.
A inference is a conclusion claimed on the basis of proof and reasoning.
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Answer:

Explanation:
From the question we are told that
Distance b/w A&B 
Frequency 
Sound speed 
Generally the equation for wavelength is mathematically given as




Generally the destructive interference X is mathematically given by


Therefore the destructive interference is

Answer: Calculate the work input in a pulley by using the previous readings in the correct mathematical equation. : Work (W) equals force (f) multiplied by distance (d), or W=fd. The work done by the pulley is the equation of weight (w) multiplied by height traveled (h).
Explanation:
Don’t know sorry I’m just trying not a good person