You aren't plotting a function, but a vector. Replace fplot by plot, or replace your input by a function. Actually, doing both will teach you a valuable lesson about aliasing.
It is always a good idea to read the documentation carefully when you are getting unexpected results or errors.
Here is a code example of both options (using subplot to show them in one figure):
disp(' Question Number 2')
f=@(x) 40./(1+((x-4).^2) + 5*sin((20*x)/pi));