Step 1: Establish the relationship between a decade and an octave.
A decade represents a tenfold increase in frequency, while an octave represents a doubling of frequency. The relationship between the two is:
\[
1 \, {decade} = \frac{\log_{10}(10)}{\log_{10}(2)} \approx 3.32 \, {octaves}.
\]
Step 2: Convert \(40 \, {dB/decade}\) to dB/octave.
Since \(40 \, {dB/decade}\) is distributed over \(3.32 \, {octaves}\), the dB per octave is calculated as:
\[
\frac{40 \, {dB}}{3.32 \, {octaves}} \approx 12 \, {dB/octave}.
\]
Final Answer:
\[
\boxed{{(1) \(12 \, {dB/octave}\)}}
\]