Each addition puzzle consists of three warships that need to be loaded with ballast so that they are balanced. Unfortunately this is impossible for one of the ships - it will keel over and sink no matter what you do. The other two ships can be loaded with ballast so they are nicely balanced.
Addition difficulty ranges from easy (1 + 4 = 5) to hard (59 + 69 + 25 = 153).
Problem solving difficulty ranges from easy to open ended.