CREATE TABLE table_68547 ("Year" FLOAT, "Chassis" TEXT, "Engine" TEXT, "Start" TEXT, "Finish" TEXT, "Entrant" TEXT)

What is the start of Offy engine and in 1972?
SELECT "Start" FROM table_68547 WHERE "Engine" = 'offy' AND "Year" = '1972'
SELECT "Start" FROM "table_68547" WHERE "Engine" = 'offy' AND "Year" = '1972'