What do the numbers 30,31,75,12 mean to Percy Jackson?

In The Sea of Monsters, Percy receives these numbers from the Three Fates (Gray Sisters). At first the numbers mean nothing to him, but later he realizes that they are coordinates for where Grover is being held with the Golden Fleece (which will restore Thalia's tree).

The three fates aren't the same as the gray sisters. The three fates are called the morai while the gray sisters are the graeae

im guessing the coordinates are to the Bermuda triangle