Its hard to follow your table data, what the units headings of the table are, and what your various definitions are. However, here's something you can do to help you figure it out: You've conducted (I assume) two assays, one for total protein, and one for lysozyme activity. By (your) definition, 100 percent purity would be some activity level (I can't figure this out from your units headings, sorry) with such low levels of total protein that the fraction is 100% -- so practice that -- make up some data, and calculate with it, until you get 100%. Then use the real data in the calculation you've determined.