To move something to the other side of the equals sign, you can use the inverse operation Left side it -9 and after transposing to right side it becomes +9
Puzzle works better with a symbolic variable in place of the addition sign. Using common terms to present falsehood prevents many from understanding unnecessarily (especially for younger students, the problem of "make these 3 equations true to solve a 4th" is different than if "presented truths" then solve equation)
