1. Do your homework: to study a subject or situation carefully so that you know a lot about it and can deal with it successfully 

CAMBRIDGE DICTIONARY:

1. It was obvious that she had done her homework and thoroughly prepared for her interview

Rõ ràng là cô ấy đã nghiên cứu cẩn thận và chuẩn bị kỹ lưỡng cho cuộc phỏng vấn của mình.

Rachel's English:

A: What attracted you to our company?

B: To be honest, what really caught my eye was your focus on growth. I was really impressed with your ambitious goals and the clear plan you have for achieving those goals. I also like the support you provide for your employees. I love your continuing education initiatives, where you pay for employees to learn new technique and skill sets. I think that really helps to build employee satisfaction and loyalty. 

A: You've obviously done your homework. ( bạn tìm hiểu rất kĩ)

2. do the job: (informal) to be effective or successful in doing what you want 

OXFORD DICTIONARY: 

Try wedging it open—that should do the job

Hãy thử mở nó ra—việc đó sẽ hiệu quả.