Answer:
351,830,000 Yuan
Step-by-step explanation:
Investment value = C$ 15.1 billion
Value in Yuan in June 2012 = C$ 15.1 billion x 6.3698 Yuan/C$
Value in Yuan in September 2012 = C$ 15.1 billion x 6.3465 Yuan/C$
The difference in Yuan if Cnooc has purchased Nexen in September instead of June is:

Cnocc saves 351,830,000 Yuan