CREATE TABLE table_50431 ("Name" TEXT, "Latitude" TEXT, "Longitude" TEXT, "Diameter" FLOAT, "Year named" FLOAT)

What's the lowest diameter when the longitude is 71.1w?
SELECT MIN("Diameter") FROM table_50431 WHERE "Longitude" = '71.1w'
SELECT MIN("Diameter") FROM "table_50431" WHERE "Longitude" = '71.1w'