Introduction:
I continue with the equations with two unknowns, but now with something easy.

The equation with the solution:

Here is the equation that I will work on:

2x + y + 3x - y = 20

The solution here is very easy, and I need to remember only one important thing:

When you have, for example, the unknown x, and you have the action:

- x + x / + x - x

Remember that this is equal to 0 every time. This is like you have one apple (+ x), and you eat one apple (- x). It is equal to 0.

And now I have + y - y in the equation; I can remove them, and it becomes like this:

2x + 3x = 20

And this is very easy to solve:

2x + 3x = 20
5x = 20
x = 20 : 5
x = 4

End:
This was actually a really short note, cause the main idea is short and easy. So, bye!