Multi IF function

Hi,

I have a list of id's, list of approval type and list of date / time against each approval type and id. 

Refer sample table below - 

Id     Approval type     Date/Time

x             a                 8/7/2015 6:44:00 PM

x             a                 8/7/2015 5:31:00 PM

x             b                 6/7/2015 5:31:00 PM 

y             a                 11/19/2015 4:36:00 PM

y             b                 11/25/2015 6:43:00 PM

y             b                 11/24/2015 8:41:00 AM

z             a                  12/4/2015 7:22:00 PM

I need to group these by ID, then approval type and then take only the latest apporoval date / time.

I am able to group them and create another table, but can someone explain how can i just filter on the latest date/time for each id and each record type within the id.

Thanks!