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**plz help solve tree problem....**

A tree is called a 3-1 tree if every vertex in the tress has degree equal to either 3 or 1.

1. Draw all 3-1 trees with four or fewer vertices of degree 3.

2. Prove that a 3-1 tree must have an even number of vertices.

3. Find a formula for the number of leaves in a 3-1 tree that has exactly m vertices.