I'm not totally sure what you are asking, but maybe this is a question about dependent and independent variables?
If so, these types of variables are used in math and science as measures. In math, independent variables and dependent variables are the "tools" used in an experiment.
Independent variables are the variables that are controlled during the experiment. These variables do not change during the experiment.
Dependent variables are the variables whose values change based on the independent variables. These variables are the "outcome" portion.
I have no idea if this answers your question or not. All I can say is that the "controlled" part of a sample would be the independent variable.
Plug in 
to each 
in the function.
Hope this helps.
頑張って!
Answer:
y = m x + b equation for a straight line
m m' = -1 for perpendicular lines
Thus m' = -1/2 is required
Check:
-1/2 * -6 + 2 = = 3 + 2 = 5 = y for the last equation give
Well you would convert the fractions to fractions with the same denominator which would make it 14/21 for the first friend and 15/21 for the second friend. But the question is asking how much is left so you have to subtract what is left in each bottle. The first friend has 7/21 left and the second friend has 6/21 left. So, the answer is 1/21.
+4 would be a vertical shift up four units. The rest of the equation is the same
