-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.