#### Answer

$g$

#### 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 $j$ is the hypotenuse of the large triangle, and $d$ is one of the legs of that same triangle. Additionally, $d$ is the hypotenuse of one of the triangles formed by the altitude of the large triangle. What we want is the corresponding leg in this smaller triangle, which is represented by $g$.
The proportion should read:
$\frac{j}{d} = \frac{d}{g}$