Usually there is about 3balls in an average can of tennis balls. Although you casn get packages of tennis balls with 18 or higher. Also comes in many shapes and sizes.
The Stars' Tennis Balls has 388 pages.
Look at the picture.
No tennis balls are not toxic. Many people may think they are but that is not true.
12 to 16
There is no set answer for that. It will depend on the make and model of the washing machine.
For every tennis match there maybe 60 balls needed
There are a great many parts to a washing machine including the door. Washing machines also have dials and barrels.
There are so many Chinese that play ping pong that I think there may be more table tennis balls.
In a usual match pack of balls there are 4 balls, but you can get tins with 2- 4 balls in them.