Table: railroad_4_6_6
Columns: railroad_quantity
class
road_numbers
builder
build_year

Question: what is the road numbers when the build year is 1943, the railroad (quantity) is clinchfield railroad (12 new, 6 secondhand)?
SQL: SELECT "road_numbers" FROM railroad_4_6_6 WHERE "build_year" = '1943' AND "railroad_quantity" = 'clinchfield railroad (12 new, 6 secondhand)'

Question: what is the road numbers when the builder is alco, the railroad (quantity) is union pacific railroad (105) and the class is csa-2?
SQL: SELECT "road_numbers" FROM railroad_4_6_6 WHERE "builder" = 'alco' AND "railroad_quantity" = 'union pacific railroad (105)' AND "class" = 'csa-2'

Question: what is the road numbers when the class is z-7?
SQL: SELECT "road_numbers" FROM railroad_4_6_6 WHERE "class" = 'z-7'