I couldn't calculate below network combination. Please help to find out the exact answer.

Question- In a point-to-point network, five routers are connected to each other. Between each pair of routers are possible to install either a twisted pair cable, an optical fiber cable or a coaxial cable. How many different combinations are there to set up this network?

My Answer was - n*(n-1)/2. Router = n
So n=5 then 5*(5-1)/2 = 10 which is false.

And I thought that I should try 2^n formula. So, if n=5 then combinations will be 32. But this one is also wrong. I am pissed of to find this solution.

It would be highly appreciated if someone can clarify me above problem and give me an appropriate solution

Thanks in Advance.