Extend to granny flat

[haybeck]

Hi everyone, my son has moved into a granny flat. The router is situated at the front of the main house. He requires wifi to the granny flat approx 20 m always. Can somebody please suggest is I should use the mesh or extender ? Or can I use both. I have very little understanding even after watching the videos
Thanks in advance

[plemans]

I'd recommend burying a wire. 

Problem with it isn't just distance, its obstruction.

exteriors of homes tend to have the materials that block wifi the best. Like metal, adobe, brick/concrete, foil lined insulation, etc. 

a mesh system might help but the problem is if you can't pick up a signal in the flat, neither will the extender/satellite.