What it`s asking is, (fraction A) plus (fraction B) should equal 1, but (fraction A) subtract (fraction B) should equal to two eighths. If you still don`t understand, please look at the diagram.
So what you have to do first is, find all the possibilities that will equal eight eighths. Please look at the following diagram.
Now, you should make all the equations subtraction questions instead of addition. Once you do that, which subtraction equation equals two eighths?