The description for this series of caches can be found on the first cache's description at https://coord.info/GC7FQYA and the assumption is made that you are doing these caches in order
From cache sixteen continue to head west along Ninn Lane. TAKE CARE as some of the cars do come along here fast.
At the given co ordinates you will see a yellow sign. Danger of -something-. Count the number of letters in that -something-, and let that number be A
-THE CACHE IS AT- N51 09 A-5 A-1 A E00 48 A+4 A+2 A-3