Suppose that someone starts a chain letter. Each person who receives the letter is asked to send it on to four other people. Some people do this, but others do not send any letters. How many people have seen the letter, including the first person, if no one receives more than one letter and if the chain letter ends after there have been $1000$ people who read it but did not send it out? How many people sent out the letter?

Form a binary search tree for the numbers $689,55,3,999,1299,1200,77,390,17,756.$

Determine the order in which a preorder traversal visits the vertices of the given ordered rooted tree.