To Solve Something, To Untie, To Untie Something
Transitive verb and Godan verb
とく
プレゼントのリボンを解くのが好きなんです。
I like untying the bows on presents.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means solve so the verb vocab version is to solve. It also means to untie and you know this verb is when you are doing the actual untying because you think it's super coo' (く) to untie things, which is why you do it nonstop.
The reading is the same as 解ける, so if you know that you can read this one too.