GATE Electrical 2014 Set 1 | Question: 45

Question

The Bode magnitude plot of the transfer function $G(s)=\dfrac{K(1+0.5s)(1+as)}{s(1+\frac{s}{8})(1+bs)(1+\frac{s}{36})}$ 
is shown below:

Note that $-6dB/octave = -20 dB/decade.$ The value of $\dfrac{a}{bK}$ is ________.