The loudness of a sound depends upon the

Explanation

using the rule of thumb, a doubling of loudness corresponds to a sound level increase of dB. Therefore,
`beta_2-beta_1=10dB=10log((I_2)/(I_0))-10log((I_1)/(I_0))=10log((I_2)/(I_1))`
Therefore, 10 machines must be operating to double the loudness.