Chap 6: Weigh the Wangdoodles with Equations!

This is a very common puzzle... for those who have not learnt algebra, they usuing try to solve the puzzle using Trial-and-Error method (or even "Guess-and-Check"). However, with Algebra, we could solve the following puzzles in a breeze by working at the problem in a systematic manner  :)

Let's read the puzzle and the brief notes in the website... Have fun weighing the Wangdoodles!
http://www.mathplayground.com/wangdoodles.html