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If Polina's earphones have a loudness of 90 decibels, the total ratio showing the loudness of the three earphones is 6+5+3 = 14
The fraction representing the loudness of Polina's earphones in the total ratio representing the loudness of the three earphones is 5/14, and if Polina's earphones have a loudness of 90 decibels, the total loudness of the three earphones is 90*14/5 = <<90*14/5=252>>252 decibels. Answer: \boxed{252}.