4 And 4

"Dart Monkey's triple shot gets 4 darts every 4th shot."

- In-game description

4 And 4 is an upgrade in the Primary Monkey Knowledge tree introduced in the initial version of Bloons TD 6. When 4 And 4 is activated, Dart Monkeys with the Triple Shot upgrade will throw an extra dart every 4th shot. To unlock 4 And 4, the player must have 5 Monkey Knowledge Points invested into the Primary Knowledge tree, and the 'Crossbow Reach' MK activated.

Summary
4 And 4 is very similar to Deadly Tranquility, with the obvious differences being it doesn't affect the Dart Monkey until the 4th shot, where the extra projectile is fired then. This MK makes Triple Shot more powerful, as 4 And 4 almost makes the Dart Monkey attack with the same amount of projectiles as the base 0-0-0 Druid attack, although much faster and without randomness on where they throw the darts.

Tips

 * Activating 4 And 4 is very important, as Master Double Cross is the next MK after 4 And 4.
 * With the extra projectile, Triple Shot can possibly do somewhat better in the earlier rounds, being able to hit more Bloons with one more dart.