Question: In 1879-81 with number built 4, what is the LMS nos?
SQL: SELECT "LMS nos." FROM "2-15412381-3" WHERE "Date" = '1879-81' AND "No. built" = 4.0;

Question: On which date was the class 157?
SQL: SELECT "Date" FROM "2-15412381-3" WHERE "Class" = 157.0;