From our computational complexity, there's a question asking to prove 3CLIQUE is decidable.The definition of 3CLIQUE is:$$\{(V,E) : G = (V,E)\text{ is an undirected graph that contains a clique of size 3}\}.$$I know this is an NP problem, and NP is a set of problems that easy to verify but hard to solve, but I don't know how to prove. Is there anyone who can help me on this? 
How to prove 3CLIQUE is decidable
graphs;computability;clique