Noun and する verb
かいけつ
トフグの株式を上場させる前に、解決しなければならない難題がまだ山積みになっている。
Before taking Tofugu public, many difficult problems that have been piling up have to be solved.
To solve the problem we decided to come up with a solution.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.