Answer
$\frac{m}{h} = \frac{h}{n}$
Work Step by Step
All three triangles are similar to one another, meaning that the sides of the triangles are proportional.
We can see that $m$ is the shorter leg of the smaller triangle formed by the altitude of the large triangle, and $h$ is the longer leg of that same triangle. Additionally, $n$ is the longer leg of the larger triangle formed by the altitude. What we want is the corresponding shorter leg of the larger triangle, which is represented by $h$.
The proportion should read:
$\frac{m}{h} = \frac{h}{n}$
