How many towers do you have to take down in co op mode

In this question, a game is being discussed, and the a question related to that game is asked. The game's name is Bloons and it is an Adobe Flash based game. This game is based on the concept of defense mechanism. It was released in 2008. In defense mechanism the player has to pop the balloons of his opponent.

Now the Co Op mode which is being asked in this question is unlocked at level 20 of this game. In this mode, you can destroy as many towers as you want. The player is given a set of 5 towers of his own just like as given to his partner.