Spring has sprung, it is time to get out and about!
At the posted coordinates you should see a faded red marble gravestone with a cross on it. The information you need is on this stone.
Let X = the number of the first letter in Mary's last name. Let Y = the number of the 5th letter in Mary's last name. (Use A=1, B=2, ... up to Z=26).
Next let A = (X x 250 - Y x 10 +6)/1000. Let B = (X x 130 + Y x 5 + 5)/1000.
Finally, add A to the posted North coordinates and add B to the posted West coordinates.