There needs to be more information.
Let's see there's forming, storming, norming and performing. I would use teambuilding during forming to limit the amount of storming in the next stage.
The number of each type of book is what is unknown, so we can represent those quantities with variables. Let x = the number of hardbacks and y = the number of paperbacks. Then we know that: x + y = 65 (the total number of books sold) We also know the total cost of both editions, which is $1356. It can be written algebraically as: 28x + 12y = 1356 We now have a system of two equations, which can be solved by substitution. It would be easier to solve the first equation for either x or y and substitute that into the second equation.