Write the equation in slope-intercept form
x-2y=4

Explanation:

Slope-intercept form means we want the y to be by itself in the equation. Every thing we do will be about getting the y alone on the left side of the equation

To start we should move x to the left hand side. We can do this by subtracting x from both sides. That way, there is an x on the right, but not the left.

x-x-2y=4-x

this gives us

-2y=4-x

Great! So now what? Well, the y isn't by itself yet because it still is being multiplied by negative two (-2). In order to move it from the left side to the right side, we have to do the opposite of multiply; divide. So, we will divide both sides by -2

-2 divided by -2 is 1, 4 divided by -2 is -2, and -x divided by -2 is

This gives us the  

Tips:

A negative divided by a negative is a positive ex: -4 divided by -2 is positive 2

If you are subtracting by a negative number, you are actually adding by a positive ex: 2-(-2) is actually 2+2

Don't be afraid to have fractions in your equations

Whatever you do to the one side of the equation, you must do it to the other side as well. Multiply the left side by 2? You HAVE TO multiply the right side by two as well. Add 3 to the right side? You HAVE TO add 3 to the left.

For problems like this (and when you have access to the internet), where you need to rewrite an equation, double check your work on desmos, which is an online graphing calculator. Input both the original equation and the equation you rewrote, and if they don't create the same line, you did something wrong.