Painting 1: the artist who painted this died in 19A3 and was born on 2B October 1881.

Painting 2: the artist who painted this was born in December 19XY. C = X+Y

Painting 3: the artist who painted this was born in June Z77W. D = W-Z

Painting 4: the artist who painted this was born in July PQRS. E =R+S-P-Q

F=A-B+C-D+E, then multiply your answer by four.
The final location of the cache is at: Cache: N 51 06.ABC W 001 59.DEF
You can check your answers for this puzzle on GeoChecker.com.