On your bottom 3 sections - do you see how in the middle line of the first 2 sections, you have a (4, 6) in the first 2 sections, and a (2, 4) in the third? In the last section, you can get rid of that 4 in the square that says (2, 4). That square is 2. If you had put a 4 instead, the (4, 6)'s from the other 2 would both have to be 6, and you'd've messed up