Answer:
a) 炎 -> 畑 -> 胃 -> 腕
炎 EN, honou - flame
畑 hatake - cultivated field
胃 I - stomach
腕 WAN, ude - arm, ability, talent, skill
b) 計 -> 古 -> 吟 -> 含
計 KEI, haka(ru), haka(rau) - plan, total, measure
古 KO, furu(i) - old
吟 GIN - sing, chant, recite
含 GAN, fuku(mu), fuku(meru) - hold, include, contain