How to reduce a huge excel file

Question

I have a short, straightforward *.XLS file with just one sheet and numerous cells with small writing on numbers. (24Kb file size)

But after making numerous changes (copying and pasting, extending formulas, saving), I removed the majority of them and created four copies of the page with minimal data.

My new file has grown to be 2.5 MB in size.

How do I find the concealed data and erase it?