Kth to last element of a singly linked list
Your code is neat, and, within the confines of the "Solution", you have solved things well.

The algorithm you use is the right one, it's implemented well, and it's all clear. I like it.

There's only one thing that concerns me. The interface of the Node class:


The value of the node should be final (not just private).
The Node class itself should be private, and should not be passed in to the findKthToLast method (it should be accessed as the private field it is)
the return value of the findKthToLast should be the node's value, not the node itself.


There are all concerns that are about the implementation environment, not just the implementation itself. The Solution concept may be the issue.

So, taking that all in to consideration, your solution, given the constraints, is a good one, but the Solution environment and requirements themselves may be the worst of the problems.