Sorry, but in my previous answer there are two typos:
fN=fo*2^N instead of fN=fo*2^2
fN=fo*10^N instead of fN=fo*10^2
About the frequency (question N. 4) you know the wave passes through the same value (5V) 200 times in 2 seconds. You have to find first if 5V are the peak value (amplitude) converting from RMS to peak. Then take into account there is only one peak each period; but for each period all other voltages are hit twice (the sinusoid increases, reach the peak, then decreases). If you draw a sketch you can figure out better.