1000 because 100 divide my 10 is 10 so just add a zero
First of all you have to make them equal to each other. What I mean is the following
3x+20=2x+40
Then you should just solve for x
For this case we must simplify the following expression:

We apply distributive property on the left side of the equation:

We subtract 3n from both sides of the equation:

We subtract 6 from both sides of the equation:

We divide between 45 on both sides of the equation:

Answer:

The closer the points are/more uniform they are to the residual line, the better the fit. The more skewed and scattered they are, the model is a worse fit.