Answer:
a) 早 -> 古 -> 吐 -> 堀
早 SOU, SA, haya(i) , haya(meru) - early, fast, hasten
古 KO, furu(i) - old
吐 TOU, ha(ku) - spew, vomit, give vent to
堀 hori - moat, canal, ditch
b) 昆 -> 皆 -> 皇 -> 現
昆 KON - elder brother, later, insect
皆 KAI, mina - all
皇 KOU, OU - emperor
現 GEN, arawa(reru), arawa(su) - present, appear, show