Answer:
a) 切 -> 召 -> 吐 -> 堀
切 SETSU, ki(ru), ki(reru) - cut
召 SHOU, me(su) - summon, wear, take
吐 TOU, ha(ku) - spew, vomit, give vent to
堀 hori - moat, canal, ditch
b) 如 -> 呈 -> 理 -> 黒
如 JO, NYO - equal, like, as, as if
呈 TEI - offer, present, exhibit
理 RI - reason, logic
黒 KOKU, kuro(i) - black