A full $m$-ary tree with $n$ vertices and $i$ internal vertices has $n = m \cdot i + 1$ vertices and $l = m − i + 1$ leaves.

How can I prove it?

I know that $m$-ary tree is a rooted tree such that every internal vertex has no more than $m$ children. The tree is called a full $m$-ary tree if every internal vertex has exactly $m$ children. An $m$-ary tree with $m = 2$ is called a binary tree

Thank you