I just looked at the spreadsheet provided by TechX2.
Enter =E5/$E$18 in cell F5 then fill down the cells in that column.
Hit the % symbol in the Number box at the top of the Excel spreadsheet.
Since you are wanting to use the value found in cell E18 for all the equations in the F column use the $ signs.
If you do not use the $ signs you will have to write an equation in each cell or if you fill down you will get an error as when you go down one cell all the cells will go down one space.
I hope this is helpful.