Imagine two right triangles. They are similar because the sun shines at the same angle or the problem wouldn't make sense with the info given.
1. shadowheight=shadowheight
2. 1.83=12x
3. Solve for x
Super-hard-impossible bonus question:
Given the information in the problem.
If you were able to stand on top of the mail box and look STRAIGHT up into the sky, the sky can represent a 2D coordinate plane. Where would the Sun be located in (x,y)?
Consider everything you know (sorry physicists)!