a piece of cake

Meaning: 楽勝だ、とても簡単なこと、楽しいこと

For Example:

‣ That history test we had in class today was a piece of cake! I'm pretty sure I got A on it.

今日クラスであった歴史のテスト楽勝やったわ！絶対A（90点以上の良い成績）や。

‣ A: Do you think you can handle this project?

B: Sure. It's a piece of cake. Leave it to me.

A:このプロジェクト対処できるかい？

　B:もちろんです。簡単ですよ。私に任せて下さい。

Synonym:

as easy as pie, a cakewalk