The above coordinates are not for the location of the cache, but are for Penny Hill.
The cache - which is a 35mm film canister - can be found at the following coordinates …
N 51 21 . 20 x (F - A) + (4 x C) - (4 x D) W 000 42 . 10 x (F - B) + C - E + 1
… where …
A = ONE
B = TWO
C = FIVE
D = TEN
E = TWENTY
F = FIFTY
Please don't leave any additional clues (subtle or otherwise) in your log.
Please could you bring something to write with, as there is no pen/pencil in the cache.
The signal at the location of the cache isn't great, so the hint should help.
You can check your answers for this puzzle on Geochecker.com.