To simplify, you just condense all of the values with the same variable, based on the signs of those values.
In this example,
6y + 5z + 8y - 3z
is the same as
6y + 8y + 5z - 3z
which can be simplified to
14y + 2z
which is the answer to your question.
Hope that helped =)
Well if you use opposite operations then you will get
mg=6
to
g=6m
320
You add all the numbers together then divide by how many numbers there was. In this case all the numbers added to 6405. You divide by 20 because there were 20 numbers. This will get you to 320.25. The closest answer choice would be 320