Question

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

Answer 1

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.)