Each lanespawner-object has a different lanenumber and a boolean variable empty..
every 0.75 seconds, first I select all lanespawners that are empty, then I pick a random instance from that selection.
That instance spawns the bullet, which also has a variable lanenumber.
This instance boolean empty is set to false and the variable lanenumber of the bullet is set to the lanenumber of the lanespawner.
When the bullet is destroyed if the lanenumber of the lanespawner is the same as the variable of the bullet, the lanespawner is set to be empty again.