In page 264, there is a table specifying the difference between male and women regarding salary. It is given in percentage and gives samples of 8 countries. I added the percentages and divided it by 8 to get an average of all countries.

After double checking the table and the calculations they are correct. The mean salary of females is only 20.3% of the males, something that is really concerning.

As a second thought, I consider that 20.3% to be the gap between salaries of male and female employees, they correct answer I think should be the difference between 100% - 20.3%, which will be 79.7%, being this the correct answer. Thus I am not sure.