user: Question: What is the River Mile with a RDB lock side and a pool length of 55.4?
Columns: ['Locks & Dam', 'Location [L ]', 'River Mile', 'Lock Side', 'Lock Lift/Drop (in feet)', 'Pool Length (miles)']
Types: ['text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['Emsworth Locks and Dam', 'Pittsburgh, Pennsylvania', 6.2, 'RDB', '18', '6.2+']
SQL:

assistant: SELECT "River Mile" FROM "Table" WHERE "Lock Side" = 'RDB' AND "Pool Length (miles)" = '55.4';