To get the answer to this problem, #6#, you have to isolate the variable. This means you have to get the variable by itself.

As you can see in the problem, the variable, #z#, is being subtracted from #9#. The first step to isolating the variable is to subtract 9 from both sides. If you do this, the 9 will disappear from the right side. This is because you performed the inverse operation of the operation that is happening.

#3 - 9 = 9 - z - 9#

#-6 = -z#

There is one more step to isolate the variable. You have to divide the variable, currently #-z#, by #-1#. This will get rid of the negative sign next to the variable. After you do this, you will have successfully isolated the variable, and have found the answer.

#6 = z#