The quickest way would require VBA, but it only takes about 10 seconds to
enter that formula, say in E1, copy it down through H20, then copy E1:H20
and paste special as values over the original range.
If you're going to be doing this very frequently maybe a VBA solution would
be the most efficient.
In some empty columns, use the formulas you have been given
Select and Copy these cells
Select A120 and use Edit | Paste Special -> Values
Now you can delete the cells with the formulas