In case Carla isn't the only name you will ever want to Sum by, what about
using the SortingGrouping box to sort by your PersonsName field, giving it a
Footer and then you can have a Sum in the Group Footer.
Or you can do the summing in a Totals query grouped by name and put the
results as a Subreport in a Report's Footer

You could also use the  DSum Function (if Carla really is the only person
being summed)
Evi