The words in red are another phrase used to describe how easy it is to do something. Someone might ask “Do you think you will be able to finish your work on time?” If the work is easy, and it will be easy to complete, a typical casual reply could be ‘It’s a piece of cake.’ The contraction ‘It’s’ combines the words ‘it’ and ‘is’.
是輕而易舉的事！（小事一樁；舉手之勞）
比方說，被問到：「你能準時完成任務嗎？」如果你覺得毫無困難，必能準時交差，則答案便是：A piece of cake!（比吃一碗雞絲麵還容易！易如反掌折枝啊！）