I am trying to make a summary of deliveries on a monthly basis

A B
1 1/11/09 20.19
2 2/11/09 19.81
3 1/12/09 25.00


i want to get the result where Nov 09 will be 40.0 and Dec 09 will be 25.0
but cant seem to make it work.
Can anyone please help me with a Formula?