It was once in a long time ago. . .
Some of us can still remember the time without mobile phones.
To make calls when you weren't home, you could go to a phone booth.
Since these phone booth are no longer really needed, you can no longer see them often.
We still have one here in Clonakilty, but there's no phone in it anymore.
The cache is at the provided coordinates and you will easily see him.
But to open the case, you have to solve this little puzzle:
Leon forgot the PIN of his SIM card
Fortunately, he still has a note with the following clues:
B + 2 = D
A - C = C
C x B = A
A / B = D
The PIN is ABCD. Crack the PIN and enter to the cache container!