Answer
4.13
Work Step by Step
When a pentagon is broken into 10 separate right triangles. each triangle will have an angle of 36 degrees in it, and each triangle will have a leg equal to half of the length of a side. Thus, we find:
$tan(36^{\circ}) = \frac{6/2}{a} \\ a = \frac{3}{tan(36^{\circ})} =4.13 $
