Work out a sum (6)
I believe the answer is:
figure
I believe this is a double definition.
'work out' is the first definition.
(I know that work out can be written as figure)
'a sum' is the second definition.
(I know this)
(Other definitions for figure that I've seen before include "Build" , "Diagram or digit" , "Come to understand - shape" , "Work out" , "form" .)