`Not sure I really understand your problem, but here's some code to help you out:`

N24; %length of zero padded fft

x=0:100;

f=sin(2*x) + sin(3*x) + sin(4*x);

Ftshift(abs(fft(f,N)));

w=-pi:2*pi/N:pi-(pi/N); %x scaled from -pi to pi

plot(w,F)

I hope that helps, feel free to e-mail me privately if you want an explanation.

N24; %length of zero padded fft

x=0:100;

f=sin(2*x) + sin(3*x) + sin(4*x);

Ftshift(abs(fft(f,N)));

w=-pi:2*pi/N:pi-(pi/N); %x scaled from -pi to pi

plot(w,F)

I hope that helps, feel free to e-mail me privately if you want an explanation.