The 2 angles are opposite each other. Therefore, they are vertical angles. This means the 2 angles are equal. So, we can set them equal to each other.
120=3x
We want to find out what n is. In order to do this, we have to get n by itself. Perform the opposite of what is being done to the equation. Keep in mind, everything done to one side, has to be done to the other.
x is being multiplied by 3. The opposite of multiplication is division. Divide both sides by 3.
