"Find the difference and simplify, if necessary."

If you can make out my work and identify my error, that would be great. The initial problem is in the top right, in Arial font. My work begins at the top left, with the equation rewritten, and continues down and to the right. If you cannot make out my work, the correct steps would be great, as well.

Also, how are symbols for equations entered directly in the post text? I don't see any format options for them.