Elegant way to add values in DataTable rows?

I have a DataTable object like following:
QTY | FirstName | LastName
30 | Tommy | Nelson
40 | Tommy | Marttern
30 | Tommy | Nelson
20 | John | Abraham

You can see that there are 1 header row and 4 actual data rows. Now I want this DT to be rearranged such that the QTY is added all together where the first name and last name match. So basically, this DT needs to be modified to something like:

QTY | FirstName | LastName
60 | Tommy | Nelson
40 | Tommy | Marttern
20 | John | Abraham

As you can see, there were 2 rows with Tommy Nelson, so the QTYs were added together, and the data row also got removed.
How could this be done elegantly? All I can think of is a very ugly way, like how you keep checking line by line and add a new row into a new DataTable object. Is there a better way than this?