Create a order 3 B-Tree for the following key data    10, 6, 12, 18, 13, 15, 3, 2, 1. What are the key values at the leaf nodes from left to write in the sequence.

To create a B-Tree, we start with an empty tree and insert the given key values one by one.

Step 1: Insert 10 into the empty tree. The tree now becomes:

     10

Step 2: Insert 6. Since the tree is not full, we can directly insert it as the left child of 10. The tree now becomes:

     10
    /
   6

Step 3: Insert 12. Again, the tree is not full, so we insert it as the right child of 10. The tree now becomes:

     10
    /  \
   6    12

Step 4: Insert 18. The tree is full, so we need to split it. We promote the middle key (12) to the parent node and create a new node to hold the remaining keys. The tree now becomes:

     12
    /  \
   10   18
  /
 6

Step 5: Insert 13. We compare it with the keys in the node and find that it should be inserted in the right subtree of 12. The tree now becomes:

     12
    /  \
   10   18
  /     \
 6      13

Step 6: Insert 15. We compare it with the keys in the node and find that it should be inserted in the right subtree of 12. The tree now becomes:

     12
    /  \
   10   18
  /     \
 6      13
          \
           15

Step 7: Insert 3. We compare it with the keys in the node and find that it should be inserted in the left subtree of 6. The tree now becomes:

     12
    /  \
   10   18
  /     \
 6      13
/ \

3 15

Step 8: Insert 2. We compare it with the keys in the node and find that it should be inserted in the left subtree of 3. The tree now becomes:

     12
    /  \
   10   18
  /     \
 6      13
/ \

3 15 / 2

Step 9: Insert 1. We compare it with the keys in the node and find that it should be inserted in the left subtree of 2. The tree now becomes:

     12
    /  \
   10   18
  /     \
 6      13
/ \

3 15 /
2 1

The key values at the leaf nodes from left to right in the sequence are: 1, 2, 3, 6, 10, 13, 15, 18.