Answer:
a) 暗 -> 章 -> 古 -> 鳴
暗 AN, kura(i) - dark
章 SHOU - chapter, badge, mark
古 KO, furu(i) - old
鳴 MEI, na(ku), na(ru)(rasu) - cry, sing, howl, ring
b) 晩 -> 勉 -> 加 -> 味
晩 BAN - evening, night
勉 BEN - effort, hard work
加 KA, kuwa(eru), kuwa(waru) - add, append, join, take part
味 MI, aji , aji(wau) - taste