I feel like an idiot.

Studying the carving you deduce that the inscription around it reveals how to open the door. If you can work out the number hidden in the puzzle, turn to the paragraph with that number.

Remember what the tribesman told you: "Back two, forward two. Back two, forward two."

I see the three arrows (top right of the skull, snake's tail & the golden piece at the bottom) but I can't for the life of me solve this. ::: spoiler I found the solution online but I still don't understand how it works.
it's 275
::: The most logical reading I can come up with is "RARA" which doesn't feel very Roman numeral-y (but Roman numerals might not even be needed.)

So... would someone be kind enough to explain this puzzle to me?