CREATE TABLE table_204_353 (id DECIMAL, "no." DECIMAL, "date/time" TEXT, "aircraft" TEXT, "foe" TEXT, "result" TEXT, "location" TEXT, "notes" TEXT)

what number is previous to 13 february 1918 @ 0915 hours ?
SELECT "no." FROM table_204_353 WHERE id = (SELECT id FROM table_204_353 WHERE "date/time" = '13 february 1918 @ 0915 hours') - 1
SELECT "no." FROM "table_204_353" WHERE "id" = (SELECT "id" FROM "table_204_353" WHERE "date/time" = '13 february 1918 @ 0915 hours') - 1