'6 F of a D' probably means '6 faces of a die' (singular of dice).
You've given the answer yourself. d=6 and f=3.
6 faces on a dice
F# G# A# B C# D# E# F# 6 sharps
Rebound central 7 (G), rebound double 6 (F), rebound double 5 (E). Is this a countdown program? Seems to be missing the central 6 (F).
c# d# f# g# a# g# f# f# f# f# f# d# c# d# f# g# a# g# f# f# f# f# f# d# f f f f f f f d# c# c# c# d# d# d# c# f f f f f f f d# c# c# c# d# d# d# c# a# a# c# d# a# a# c# d# f f f f f f f d# c# c# c# d# d# d# c# f f f f f f f d# c# c# c# d# d# d# c#
c# d# f# g# a# g# f# f# f# f# f# d# c# d# f# g# a# g# f# f# f# f# f# d# f f f f f f f d# c# c# c# d# d# d# c# f f f f f f f d# c# c# c# d# d# d# c# a# a# c# d# a# a# c# d# f f f f f f f d# c# c# c# d# d# d# c# f f f f f f f d# c# c# c# d# d# d# c#
6
d e f# f# f# d e f# f# d e f# a g f# f# e f# d d e f# f# e d d b f# e d d a d d a d e f# d a d e f# f#
Assuming its 100 % efficient, then f * d = f * d, then 2 * 6 = 4 * d so, (2 * 6) / 4 = d, then 3 = d so d = 3 metres
D f d# d f d# e f e f e c a a d g a a d f g e d f d# d f d# e f e f e c a a d f g a a d
It has 6 sharps, but if you are referring to the scale it goes f#, g#, a#, b, c#, d#, f, f#
C g g f g f c c d d c d f g a g f c c g f d c g g f g f c d d c d f g c c a g f c a g d f a g f c a g f g c f e d c e d c d f a g f d d f a g c d f f a g f d f g c g g f g f c c d d c d f g a g f c a g f d c g g f g f c d d c d f g c c a g f c a g d f a g f c a g f g c f e d c e d c d f a g f d d f a g c d f f a g f d f g c g f g f g f c c d f c d f c g g-f g-f g-a-f c d f c d f c g g-f g-f g-f-d c d f c d f c g g-f g-f g-a-f