Table: locomotive_specs
Columns: gauge
railway
class
works_no
year
builder

Question: Which year has a railway class of 250?
SQL: SELECT "year" FROM locomotive_specs WHERE "class" = '250'

Question: Which works number has a class of 15th and year of 1940?
SQL: SELECT "works_no" FROM locomotive_specs WHERE "class" = '15th' AND "year" = '1940'

Question: Which builder has a railway of Rhodesia Railways?
SQL: SELECT "builder" FROM locomotive_specs WHERE "railway" = 'rhodesia railways'

Question: Which railway has a class of 250 and year 1936?
SQL: SELECT "railway" FROM locomotive_specs WHERE "class" = '250' AND "year" = '1936'