A) no cosine/sine rule here..
[(n-2) * 180]/n = angle of 1 vertex = x
n = number of vertices (6)
B) draw lines from each vertex to the center of hexagon so you'll see the triangles.
all sides of a chosen triangle are the same length = a
((a^2 = a^2 + a^2 - 2 * a * a * cos (x/2)
x = the angle you calculated in A) section. << just to show the cosine rule.. you get nothing from that without knowing a))
better way is to use this.. 2 * [(a * sqrt (3))/2] = 7
you can compare the results.. should be the same.
C) what's a guttering? xD