http://140.78.137.200/ifac50/Project...content42.html

if you scroll to the bottom, then up a liitle you see a table. how did they find GAIN K?

and how would i find it for my example: 40K / s(s+3)(s+5)

 

Perhaps your question should ask for the gain K at a given frequency. For instance, the gain of your example at DC is infinite - due to the pole at zero frequency. At infinite frequency the gain is zero.