The expression is,
(Inverse property of addition: ) \ \
(Identity property of addition: ) \ \
The sum is 6.
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=5e6c7c040b315b90b54fedaad2a385c6.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=9585e41b9a890e9db984ddadfad77e1e.png\")
(Inverse property of addition: ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=97348cc413a47b54636ad1c2df1d00ae.png\")
) \ \
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=b2d202faac0f2658fd141425a56f8983.png\")
(Identity property of addition: ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=407e45279b665d90841e082d419c0af9.png\")
) \ \
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")