Final answer:
Cosmo overcame the mental set that was blocking his problem-solving by taking a break, which allowed for incubation, leading to his 'Eureka moment' which is an insight that emerged during the period of rest.
Step-by-step explanation:
When Cosmo jumped out of his bath shouting "Eureka, I solved the problem!", what helped him overcome the block in solving the calculus problem was incubation, which helped him get past the mental set that initially impeded the solution. The break he took allowed his subconscious to process the problem without the pressures of active, conscious thought, a process that is sometimes impeded by a mental set, which is an inclination to approach problems in a certain way based on past experiences.
In problem-solving, a mental set can be an obstacle because it limits our thinking to familiar patterns and procedures which may not lead to a solution. Incubation is akin to taking a mental step back to allow the mind to unconsciously work through the problem, which can often lead to insights.
Here, Cosmo's 'Eureka moment' exemplifies the cognitive process where distancing oneself from the problem can facilitate the breakthrough needed to find a solution.