Reasoning, Inference
noun, verbal noun, の adjective
To infer reason is to have reasoning.
すいり
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
日付の書き方から、その脅迫状はアメリカ人によって書かれたものだと推理しました。
I inferred that the intimidating letter was written by an American due to the way the date was written.