Answers

2014-09-25T17:49:28+08:00
The X and Y you need to put a number in X and Y
  Ex.
   3 + 1 = 4
   4 + 2 = 6

The X,Y, is a blank number
any letter , don't worry
if it is E + G that is blank number again
1 5 1
2014-09-30T18:12:38+08:00
It is very simple X+Y = Y+X because you can not add unlike terms unless this variables has correspondent number for example :
X= 2
Y= 3
then X+Y=
2+3=5 
hope that helps 
and also X+Y is not equals XY many people always get confuse and will answer XY and that's wrong because XY is basically saying X times Y and X times Y is not the same as X+Y 
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