Whole problem (3)
I believe the answer is:
sum
This clue is a double definition.
'whole' is the first definition.
(sum is a kind of whole)
'problem' is the second definition.
(arithmetic problem)
(Other definitions for sum that I've seen before include "maths problem" , "Total; problem" , "Quantity obtained by addition" , "Quantity of money" , "Add together" .)