How to set out a three line profit and loss account?

I am writing a letter to claim exemption from previous years national insurance as i didn't earn enough to pay tax or national insurance. When i spoke to HMRC they said just to write them a letter and include a three line profit and loss account for those couple of years.

What is a three line profit and loss account? and how do i set it out on a simple excel spreadsheet to send them?

Thanks