b+ tree

Question

A B+ tree of order 'd' is a tree in which each internal node has between 'd' and '2d' keys values. The root has between 1 and '2d' values. What is the maximum number of internal nodes in a B+ tree of order 4 with 52 leaves.
A. 8                                     B.13
C.17                                    D.19

Comments

For 50 leaves ,the no. of internal nodes should be 13.Ie. 1+2+5+5+25+25.ie.13 internal and 50 leaves.

1--> root

level 2 -  2 nodes 

level 3 - 2*5 nodes

level 4 - 10 * 5 nodes (leaves)

internal node = 1+2+10 = 13

where i am wrong?

---

in b+ you should evaluate from bottom..

---

how can you please  explain i am not getting what u saying.