CREATE TABLE table_66670 ("Name" CLOB, "Employed" CLOB, "Position held" CLOB, "Honour" CLOB, "Citation" CLOB)

What are the years employed shown for mathematics & prefect master?
SELECT "Employed" FROM table_66670 WHERE "Position held" = 'mathematics & prefect master'
SELECT "Employed" FROM "table_66670" WHERE "Position held" = 'mathematics & prefect master'