Help with an equation please.

I have got the formula (it is beginner economics) and I cannot figure out, how to get from the first to the second line. I know that you need to take some of the figures from one side of the equation, but I just can't understand which ones.

The first line: 20=Qc+2Qf.

And that's the second line: Qc=20-2Qf.

How do u get to the secone line.

Thx a lot.

If 20 = Qc + 2Qf we can say
Qc + 2Qf = 20
- 2Qf = -2Qf subtract -2Qf from each side of the equation and we have
Qc = 20 - 2Qf

What is being done here is that we are subtracting 2Qf from each side which results in there being no 2Qf on the Left Hand Side and a negative 2Qf appearing on the Right Hand Side.

In practice (in my case anyway) the 2Qf is moved from LHS to RHS and the sign changed which of course amounts to the same action only it is not thought through every time as to exactly why this is so. Having satisfied yourself as to why is so, then it is not really necessary to think about it beyond that "You can move a term across the equals sign but you must change the sign"

20=Qc+2Qf subtract 2Qf from both sides you get the second line Qc=20-2Qf

20-2Qf=Qc+2Qf -2Qf

20-2Qf=Qc

Yes you are correct.Subtracting 2Qf from each side is the same as taking it to the other side and changing its sign.The same thing,

Hope everything is clear now.If so pick my answer :)

20 = Qc + 2Qf
20 - 2Qf = Qc
Qc = 20 - 2Qf