This is a simple 2-stage multi-cache. The posted coordinates will bring you to a brick monument with a plaque in the Rainham White Church Cemetery.
From the plaque, find the year the first evangelical church of the black creek circuit was built. From that number subtract 1809 and divide the result by 1,000. Add this number to the posted North Coordinates.
From the plaque, determine the number of churches that have been built here over the years. Divide this number by 1,000 and add the result to the posted West Coordinates.