user: Question: What is the sum of Year opened when steel was the material with a Span feet of 1476?
Columns: ['Rank', 'Name', 'Span metres', 'Span feet', 'Material', 'Year opened', 'Location', 'Country']
Types: ['real', 'text', 'real', 'real', 'text', 'real', 'text', 'text']
Sample row: [1.0, 'Chenab Railway Bridge', 460.0, 1509.0, 'steel', 2017.0, 'Reasi ( Jammu and Kashmir )', 'India']
SQL:

assistant: SELECT SUM("Year opened") FROM "Table" WHERE "Material" = 'steel' AND "Span feet" = 1476.0;