Solutions :

3-letter words (1 point): 27

DUE; EMU; ERR; FUD; FUM; FUR; IRE; JUD; JUT; MET; MEU; MUD; MUT; REI; REM; RET; RIT; RUD; RUE; RUM; RUT; TIE; TUM; UDS; URD; UTE; WUD.

4-letter words (1 point): 35

DRUM; DUET; DURR; ERRS; FUDS; FUME; FURL; FURR; FURS; FUTZ; ITEM; JUDS; JUTE; MERI; MUDS; MURL; MURR; MUTE; MUTI; RIEM; RITE; RITZ; RUDS; RUER; RUME; SWUM; TIER; TIRE; TIRR; TRIE; TRUE; TURD; TURF; URDS; WUDS.

5-letter words (2 points): 14

FUMER; FUMET; FURLS; MERIT; MURLS; MURRE; MURRI; MURTI; MUTER; TIRRS; TRUER; TURDS; TURFS; UTERI.

6-letter words (3 points): 2

DURRIE; RETURF.

7-letter word (7 points): 1

RETURFS.