This is the 7571st most frequent Japanese word.
分り
"分り" (わかり, wakari) means "understanding" or "comprehension" in English.
Here, "分り" is part of "分りやすい" (easy to understand), conveying the comprehensibility of the subject discussed.
彼の話は分りやすかった。
His explanation was easy to understand.
In this sentence, "分り" is used in "分りません" (do not understand), indicating a lack of comprehension regarding the answer.
その問題の答えが分りません。
I do not understand the answer to that problem.
The word "分り" inside "分りました" (understood) shows the action of coming to an understanding about someone's intention.