Table: railway_vehicles_4
Columns: number_name
description
current_status
livery
date

Question: Which Livery has a Description of 20t tanker, with a date later than 1941?
SQL: SELECT "livery" FROM railway_vehicles_4 WHERE "description" = '20t tanker' AND "date" > 1941

Question: What's the Description for Scottish Tar Distillers No. 78, that's Livery is black, and a date prior to 1897?
SQL: SELECT "description" FROM railway_vehicles_4 WHERE "livery" = 'black' AND "date" < 1897 AND "number_name" = 'scottish tar distillers no. 78'