If both waves have the same wavelength, then the amplitude of their sum could be anything between 1 cm and 9 cm, depending on the phase angle between them.
If the waves have different wavelengths, then the resultant is a beat with an amplitude of 9 cm.
Oooooo, that statement is not true. Countries create quotas and tariffs to <em>LIMIT</em> the volume of trade with other countries, including their neighbors.
