Once you have determined what is missing, use substitution (Z=26, J=10, etc.) to determine a value, "P".
Now for the math. . .
X = P / 1000
The final can be found at the following coordinates:
N 43 (41.549 - X) W 079 (34.311 + P)
Read the calculation carefully, ESPESCIALLY FOR WEST COORDINATE
You can check your answers for this puzzle on GeoChecker.com.
This cache is a short walk away from the posted coordinates, and is kid-findable. Also, be wary of small flying white orbs...I spotted one at the GZ when I placed the cache.