user: Question: What is the total launch failures when there are 4 launches, and the not usable is greater than 0?
Columns: ['Block', 'Launched', 'Operational', 'Not usable', 'Retired', 'Launch Failures']
Types: ['text', 'real', 'real', 'real', 'real', 'real']
Sample row: ['Block I', 11.0, 0.0, 0.0, 10.0, 1.0]
SQL:

assistant: SELECT SUM("Launch Failures") FROM "Table" WHERE "Launched" = 4.0 AND "Not usable" > 0.0;