Answer:
a) 早 -> 古 -> 吐 -> 堤
早 SOU, SA, haya(i) , haya(meru) - early, fast, hasten
古 KO, furu(i) - old
吐 TOU, ha(ku) - spew, vomit, give vent to
堤 TEI, tsutsumi - bank, embankment, dike
b) 炎 -> 畑 -> 里 -> 坂
炎 EN, honou - flame
畑 hatake - cultivated field
里 RI, sato - village
坂 HAN, saka - slope, hill