How to input text into a cell without the text function

I inherited a spreadsheet from another employee and there is a cell in the spreadsheet that appears empty but when I type a number into it, it always returns that number with the word "Days" next to it. IE....I enter "300"....."300 Days" shows up in the cell. The cell can be used as if only 300 were in it...IE...it will calculate as part of another formula or function.

How did the other employee do this?

Thanks

Nevermind, I figured it out. He used a custom format in that cell.

Thanks