Going to the posted coordinates will not help you but they are required to complete the math. They are the starting numbers to use in your math calculations. You can find the BM page using Waymark.com or you could do some simple searching to find the info needed. Ok we are at the BM, or you found an image, right?
Now for the math.
North. Subtract 300 from the number following the A on the BM (A???) and add the answer to the posted North coordinates.
West. Start with the four digit number on the BM and subtract 715. Then divide by the single digit which appears twice in the four digit number on the BM and add the answer to the starting West coordinates. You should now have the final coordinates.
Go find the container. Watch out for the drop-offs, snakes, loose rocks, and the fox-tails on your short hike out.