US agent bored when adding up (3)
I believe the answer is:
fed
'us agent' is the definition.
(short for a federal agent)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for fed that I've seen before include "supplied with power?" , "US agent" , "Banking authority" , "Given food to eat" , "American cop" .)