Table: locomotive_gswr
Columns: class
date
builder
no_built
1919_nos
lms_class
lms_nos

Question: In 1879-81 with number built 4, what is the LMS nos?
SQL: SELECT "lms_nos" FROM locomotive_gswr WHERE "date" = '1879-81' AND "no_built" = 4

Question: On which date was the class 157?
SQL: SELECT "date" FROM locomotive_gswr WHERE "class" = 157