 Delete key entry 7:
There is an underflow....
 The sibling node has
1 entry
⇒ we must use a
merge operation:
There is another
underflow....
This time, the
sibling node
has only one entry (15)
So we must perform
another
merge operation....
 We perform a
merge operation:
There is another
underflow....
Again, the
sibling node
has only one entry (70),
and we must perform
another
merge operation....
But now,
we have reached the root node !!!
 The merge operation that
merges with the root node
will reduce the height
of the 2,4tree !!!

 Observe the
merge operation
with the
root node:
 There is no more parent node,
so we replace the
root node:
DONE !!!
