I was looking at muckypuppy4's maths homework the other night, which you can find below, and was a little disappointed that he had made a mistake. He had done quite well having shown a clear, correct method but had made a slip at the end and thus lost a mark. However he did provide the inspiration for this cache.
The cache is at:
N51 11. M(12) + M(7) + M(6) - M(1)
W000 38. M(10) + M(8) +M(4) - M(2)
I think you will know if you have solved this puzzle but as a check, the sum of all 15 digits is 39