The figure below shows the bode magnitude and phase plots of a stable transfer function
G(s)=n0s3+d2s2+d1s+d0
Consider the negative unity feedback configuration with gain k in the feedforward path. The closed loop in stable for k<k0. The maximum value of k0 is
For G(s)
MdB(ωpc)=20 dB
When cascaded with k,
GMdB=−20 dB−20log10(k)>0 dB
20+20log10(k)<0
20log10(k)<−20
k<10−1=0.10
So,k0=0.10