How much more total box office gross did the Walt Disney Company have in revenue in 1998 than in 1997?
SUBTRACT(SUM(Year = 1998), SUM(Year = 1997))
SELECT SUM(CASE WHEN `Year` = 1998 THEN Total ELSE 0 END) - SUM(CASE WHEN `Year` = 1997 THEN Total ELSE 0 END) FROM revenue