Page 551 Exercise 16

Since x is simply the minimum number of children within a node, the formula for the number of nodes states that the number of nodes in the tree equals 1 + the number of keys divided by the minimum number of keys/ node.  This is fairly obvious.
 
The depth formula states that: depth ≤ 1 + log_{mininimum number of keys}^{{ (n+1)/2}}.

Since the N nodes are split three ways rather than 2, this  formula actually overestimates the depth. We can also say that depth ≤ 1 + log_{minimum number of keys}^{(n+1)/3}.