Subtract the mass of the filter paper (0.27 g) from the mass of the paper and copper (0.98 g). record the difference in the data table as the amount of copper.

When measuring copper that is collected on a filter paper, the mass measurement obtained will include both the mass of the filter paper and copper.
therefore we have to find the mass of the empty filter paper before copper is on the paper.
the mass of the filter paper alone is 0.27 g
then the mass of copper and filter paper is 0.98 g
therefore to find the mass of copper alone we have to take the difference between the 2 masses
mass of copper = (mass of copper + filter paper ) - mass of filter paper
                          = 0.98 g - 0.27 g 
mass of copper = 0.71 g