Answer:
a) 訟 -> 翁 -> 翌 -> 竜
訟 SHOU - accuse
翁 OU - old man
翌 YOKU - next, following
竜 RYUU, tatsu - dragon
b) 計 -> 古 -> 員 -> 贈
計 KEI, haka(ru), haka(rau) - plan, total, measure
古 KO, furu(i) - old
員 IN - member
贈 ZOU, SOU, oku(ru) - give, present, bestow