Effect of negative feedback on Amplifier
If the amplifier is capacitively coupled this affects the lower frequencies that can pass. As originally quoted the low frequency cut-off point is 100 Hz and this is where I have a problem with the solution. No matter what extra applied feedback is introduced, that LF cut-off is going to remain at 100 Hz.

Think of an inverting op-amp configuration: -



The LF cut-off is dictated by C and R1 attached to the inverting input (a virtual earth) and you can reduce R2 as much as you want and it won't alter this fact.

How about a non-inverting amplifier: -



In this type of amplifier the LF cut-off is defined by C and Rbias and no amount of fiddling with R1 and R2 is going to alter this.

So, for the amplifiers I have shown above, the LF cut-off remains at 100 Hz.

For the HF cut-off, if the gain is reduced (by feedback) from 1000 (60 dB) to 10 (20 dB) and it is assumed that the gain-roll-off slope is 6 dB per octave (20 dB per decade) then you get a new HF cut-off of 100 kHz: -