I don't get these problems, can someone help me out?

1. Jeff added two fractions. Lydia subtracted the same two fractions. Jeff's answer was 3/4 greater than Lydia's. What could the fractions be?

2. To calculate 7 1/8 - 2 2/3, Lee added 1/3 to 4 1/8. Why do you think that Lee did this?

The answers/solutions/equation to these are simple but I can't seem to get a hold of them :( please help. Thank you! :)