So your plane will land in Monastir ? in the afternoon and you wanna be in the evening in Tunis ...
I think the best way is to get a taxi from Habib Bourguiba Airport to Sousse exactly in sousse to the Louage Station ( in Bir Chibak ) and there you will find a lot of Louages going to Tunis ... you won't miss it .. i mean it's easy to find ...
I think this's the good way to do it but not the best
...
Good luck
Makrem