I have been given some homework in my precal class involving delta-epsilon proofs. I understand how to do them for the most part, but I am confused about proving the limit of a horizontal line.

Here is one of the problems he gave us:

lim 3

x->6

We are supposed to prove it, but the method he has taught us to follow does not seem to work. I hope it isn't something really simple i just haven't thought about but nobody in the class has figured it out definitively in the two days we have had to work on the problems while our teacher has been away at workshops.