And you're sure it's not a trick question and he's trolling you ?
If that's serious, there's several aspects to it:
- if one track is mono, then panning it both left and right will change precisely nothing
- if one track is stereo, you may further widen its image with the Stereo Spread plugin although this gets ugly pretty quick. *Always* check for phase problems in mono when trying this kind of stuff
- to create "three more horns", pan the first three to the left, duplicate the tracks, pan those right and either use three Modulation Delays with some random modulation or three Automatic Double Track plugins (the Waves REEL ADT is pretty good) if the tracks are audio, or slightly randomize the MIDI notes and maybe use very slight instrument detuning in case you have MIDI parts.