It's a piece of cake

fall behind - mieć zaległości
I'm really stressed out when I fall behind with my work.

catch up on - nadrabiać (zaległości)
She has been ill and has to catch up on school work.

get down to work - zabierać się do pracy 
He sometimes finds it difficult to get down to work.

take in (information) - przyswajać (informacje)
It's sometimes difficult for students to take in infrmation in a lesson.

feel out of your depth - całkowicie się pogubić
Tom felt totally out of his depth in Maths and couldn't undestand the topic.

a piece of cake - łatwizna
This exam was a piece of cake.

burn the midnight oil - pracować do późna w nocy
Anna is a night owl and often burns the midnight oil.

know something inside out - znać coś na wylot
He is an expert and knows this subject inside out.

pass (an exam) with flying colours - zdać (egzamin) śpiewająco
It was the most difficult exam but she passed it with flying colours.

coat - Zara (old collection)

bag/boots/bow - Zara

blouse - Mango (old collection)

belt - H&M