B-Tree - predecessor/minimum key

Explain how to find the minimum key stored in a B-tree and how to find the predecessor of a given key stored in a B-tree.

This is what I have so far, but I have no idea if I am even correct:

Finding the minimum key stored in a B-tree is quite simple, we just do the opposite of find the maximum and that would be by finding the left most leaf / subtree for the given root. Once, we find the left most leaf / subtree of the give root the smallest element in the node would be the minimum key.
Finding the predecessor first we would have to find the maximum