Add (4,2)

(Another definition for tack on that I've seen is " Affix by stitching".)

(Other definitions for append that I've seen before include "Add on at the bottom - say signature" , "Add on, attach" , "Adjoin" , "Add, annex" , "provided as add-on" .)

(Other definitions for tot up that I've seen before include "Determine the sum of" , "Add (some numbers)" , "Do summer job" , "Count" , "Add together (driving offences)" .)

(Other definitions for affix that I've seen before include "Attach" , "Fasten (to something)" , "Glue" , "Join" , "Stick on" .)