The Bloon Solver is the final upgrade of Path 1 for the Glue Gunner in BTD6. It allows the glue fired to dissolve Ceramic and M.O.A.B. Class Bloons twice as fast. It also allows the Glue Gunner to fire much more quickly, roughly x4 faster, along with gaining a powerful Glue Splatter ability that allows it to hit up to 12 bloons, 16 with Glue Splatter and 18 with Splatty Glue. However, it can only hit 1 MOAB-Class Bloon at a time. It costs $20,400 on Easy, $24,000 on Medium, $25,920 on Hard, and $28,800 on Impoppable.
It is recommended to buy the 5-2-0 Glue Gunner instead of the 5-0-2 Glue Gunner becuase the Glue Gunner already destroys bloons so quickly and it does such insignificant damage and slow-down to M.O.A.B-Class Bloons that allowing it splash more bloons is simply more effective against its primary target, bloons.
The artwork shows that the tank on the monkey's back is not a glue container. It is believed to be an oxygen cylinder as its pipes are connected to its mouthpiece not the gun and it has glue containers on the gun. This shows that the fumes of the super corrosive glue are so toxic that they can't even be breathed with a gas mask and the monkey constantly needs to breathe from an oxygen tank.