The intensity of a 70-dB whistle is quintupled. What is the new decibel level

Multiplying the power of any signal by 5 can be described as

an increase of 6.99 dB.

If the whistle blew at 70 dB initially, and its sound power became

multiplied by 5, and the whistle and the listener both stayed in

the same places, then the listener would tell you that the whistle

was now blowing at 76.99 dB.

(More likely, he would report "77 dB" as he held his ears and winced.)