Could you please explain this question with steps , thank you!

You estimate that you will need to supplement your retirement funds with an additional $30,000 per year. You estimate that you will be in retirement for 25 years, and you have 30 years to save for your retirement. You can either save annually, or monthly. In either case your funds are invested in an account that will earn 7% per year compounded monthly; your funds will remain in this account while you are retired as well. Which is better (mathematically) to save annually or monthly? 25 years in retirement 30 years until retirement Save annually Need $30,000 per year Or Save monthly I 7%, compounded monthly during both time periods