We have the following:
The formula is the following
[tex]d=10\log (\frac{P}{P_o})[/tex]From what the statement tells us, the value of d is equal to 20, now we replace and solving for P / Po
[tex]\begin{gathered} 10\log (\frac{P}{P_o})=20 \\ \frac{10}{10}\log (\frac{P}{P_o})=\frac{20}{10} \\ \log (\frac{P}{P_o})=2\rightarrow\log (x)=2\rightarrow x=10^2\rightarrow x=100 \\ \frac{P}{P_o}=100 \\ P=100\cdot P_o \end{gathered}[/tex]Therefore, the sound of the horn is about 100 more intense than the weakest sound heard to the human ear.