We can first find the area of a hexagon. If we break it into 6 equilateral triangles, we can calculate their areas. Let's say the side length of the regular hexagon is s. The area of one of the equilateral triangle is s2√34, so the area of the entife hexagon is 3s2√32. Because we know the area is 3, we can solve for s:
3s2√32=3 ==> 3s2√3=6 ==> s2√3=2 ==> 3s2=2√3 ==> s2=2√33
This is best I can go. It get's really complicated if you go even further. Please let me know if I made a mistake.