How to use fourier transform in simulink

Hello, im new to simulink Im asked to find the magnitude spectrum of input X(w) and the output signal Y(w) on the same graph. If my input is a continuous square wave with magnitude -+1V and fundamental frequency 130 rad/s And its a question about designing a 3rd order low pass butterworth filter. how can i plot the magnitude spectrum in the frequency domain?

Answer 1

[Ahmed raafat]

I remember i saw fft block before in simulink

[Group 1]

Yes, but how do i plot it?