What is the missing number?
–3.4 + (–8 + 2) = [ _ + (–8)] + 2

-3.4 + (-8 + 2) = ( _ + (-8) + 2)
-3.4 + (-6) = ( _ + (-8) + 2)
-9.4 = ( _ + (-8) + 2)
-9.4 = ( _ + -6)
Now remember whatever you do to one side you have to do to the other. :)
-9.4 - -6 = -6 - -6
= -3.4
You had to do one side of the equation before you could do the other side because you needed an answer to follow. 

9/12 is the answer because 3/4 times 3 each is 9/12