Notch filter with 4 Hz Bandwidth
A Design Spec for any Active Filter must include many variables.

Gain PassBand  ( I used 3dB )
PassBand Ripple
PassBand BW  ( not defined here ) and relates with PassBand ripple or gain error
Attenuation BandStop  ( 1/20 = -26 dB needed at 100Hz)
BW Bandstop ( not defined here which relates to 100 Hz signal f error. (I used 4Hz)

Some variations in spec desciptions may exist, but must define all important     limits needed.
My specs
Pass Band gain: 1.5  ( 3.522 dB )
PB Ripple max: 1dB
center frequency : 100 Hz
Corner frequency attenuation 0.5 dB
Stages : 2   4th order
Input DC offset; minimal

This exceeds the requirements by a wide margin. and can be further optimized by offseting each notch e.g. +/-2 Hz if a wider/deeper f bandstop depth is needed.
Filter.exe Tools exist (free) at ti.com to design anything in minutes.
The secure https :// goo.gl/cHNTYx leads to my simulator above so you can change parts in real time. Java must be enabled .