Spectrum analysis (Fourier)

[Aries]

Hello everyone,
let's suppose we have the following signal: f(t)=4+(4/pi)*sin(2*pi*800*t)+(4/(3*pi))*sin(2*pi*2400*t)+(4/(5*pi))*sin(2*pi*4000*t).
Ok, this is the resulting waveform (time domain, 4 is the average value):



Now the (banal) question is, how can I determine (i.e. to plot) the spectrum (in the frequency domain) of the function on the Prime, something like this below ?



Any hint would be helpful.
TIA and best,

Aries