What is the highest number of not usable satellites when there are more than 0 launch failures, less than 30 retired, and the block is I?
CREATE TABLE "satellites_by_block" (
  "block" text,
  "launched" real,
  "operational" real,
  "not_usable" real,
  "retired" real,
  "launch_failures" real
);
SELECT MAX("not_usable") FROM "satellites_by_block" WHERE "launch_failures">0 AND "retired"<30 AND "block"='block i';