What is the difference in size between the Long Island, NY and Northvale, NJ facility in sq ft?
{"Long Island, NY": {"Size (sq. ft.)": 93000, "Own or Lease": "Lease"}, "Garden Grove, CA": {"Size (sq. ft.)": 27850, "Own or Lease": "Lease"}, "Tianjin, China": {"Size (sq. ft.)": 28000, "Own or Lease": "Lease"}, "Northvale, NJ": {"Size (sq. ft.)": 9000, "Own or Lease": "Lease"}}
size_long_island = df["Long Island, NY"]["Size (sq. ft.)"]
size_northvale = df["Northvale, NJ"]["Size (sq. ft.)"]
answer = size_long_island - size_northvale