To find this cache you need to visit the cache Alphabet S - Sound of Music (GCN678) first. There you will find the values of A and B.
The given coordinates have nothing to do with the cache. You need to find out who initially said the following three sentences:
Quotation “C”: “Die Strategie ist der Gebrauch des Gefechts zum Zweck des Krieges.” Take the last letter of the last name (surname).
Quotation “D”: “Quod scripsi, scripsi.” Take the first letter of the name.
Quotation “E”: “Apostreyon thn macairan sou eiV ton topon authV, panteV gar oi labonteV macairan en macairh apolountai.” Take the first letter of the English first name.
All questions refer to the person who said or wrote the sentence initially—not necessarily in the language of the quotation. Convert the three letters into numbers (A = 1, B = 2, …, Z = 26). Let us signify the three numbers by C, D, and E. Calculate
xxx = 291 + A + B + 10 * (C + D + E) and
yyy = 307 + A – B + 10 * (C + D + E).
If either xxx or yyy has more than three digits, drop out the thousands and use the three least significant digits only. The cache is located at N 60° 13.xxx’ E 24° 41.yyy’.