No of samples 4mega samples per second,using 8 bit ADC,V p_p is6V. calculate frequency and peak power
There are sam samples per second and 8 times less pure sine cycles per second. This means that there are sam/8 pure sine cycles per second. 

What shannon has to do with that? Probably you mean that Niquitz allows you to reduce sampling, make it 4 times more rarely, as low as sam/4 samples per second. That would sample twice per sine period.