CREATE TABLE table_204_939 (id NUMBER, "year" NUMBER, "chassis" CLOB, "engine" CLOB, "start" CLOB, "finish" CLOB)

in 1979 how many places did the cosworth engine decrease from start to finish ?
SELECT "finish" - "start" FROM table_204_939 WHERE "year" = 1979 AND "engine" = 'cosworth'
SELECT "finish" - "start" FROM "table_204_939" WHERE "engine" = 'cosworth' AND "year" = 1979