Question 261430
Those lines are absolute value bars. Simply think of them as parenthesis (just don't erase them or distribute). With {{{abs(7-4)}}}, you simply look at {{{7-4}}} and subtract to get {{{3}}}. So {{{abs(7-4)=abs(3)}}}. 



Now here's a very critical thing to remember: the absolute value of any number is ALWAYS positive. Think of it as the distance from that number to zero on the number line. So in our case, {{{abs(3)=3}}}. Another example is {{{abs(-3)=3}}}



So {{{abs(7-4)=3}}}



As for the second part, I'm not sure of what you're asking. You just want to add 2+2 right? If so, then 2+2=4. In addition -2+2=0 since we can rearrange the terms to get 2-2=0.