So you do 20%*426 to get 85.2 then you would subtract 85.2 from 426 because they sold 20% more than last year. On top of that the answer isn't 355 it is 340.8.
You first subtract 4 from both sides. Then you divide both sides by -8 (note: when you multiply or divide by a negative the sign flips. Then you get your answer