In both EX and QP, you can choose whether the chart will be attached to your present sheet or added separately. More details are given in Spreadsheet Project 6. The graph will be printed. There are many options to customize your printout, explore the menu to see what your choices are. Printout a copy of your spreadsheet to turn in.
Floppy disks are reliable and if they fail only a few files are lost.
If the hard disk fails, you lose the equivalent of 50 to 100 floppies. A floppy disk will remain under your control. Any of your files saved on the hard disk in the lab will be subject to erasure by someone else. At most then, you would have to re-do no more than 15 minutes of your work. Make a habit of saving often.