The best method to separates mixture of salt and water is evaporation. Take a small sample of mixture in a china dish. Heat it till all water evaporate. The residual remain is salt. Josh should use this method to separate salt from water.
When crest of one wave interferes with the trough of other wave, the amplitude of the resultant wave formed is less. Hence the type of interference is destructive interference.
Answer:
S = 2 π R
R (mean) = 92.9E6 miles
S = 2 * 3.14 * 92.9E6 miles = 5.84E8 miles
