OK thanks.
Which exact model is the G3? Which version of Mac OS?
Depending on the model, you may have to buy a USB floppy drive, and copy them via floppy disks.

Or, if you can connect at all to email on the G3, you could try emailing the files to yourself.
Because Microsoft Office 4.2 (Excel 4.0) is almost 25 years old, you may have some issues opening them, and with macro compatibility.
C