Hello! What you can also do is:
16.8 = 2(3.6) + 2w (I know same equation :D)
16.8 = 7.2 + 2w
Then take 7.2 away from both sides: 7.2 - 16.8 = 7.2 + 2w - 7.2
This should be your answer: 9.6 = 2w
Then just divide 2 from both! 9.6/2 = 2w/2
You should get the same answer! 4.8 = w
It was a lot simpler to do it this way! Anyways, have a great day!