(arithmetic) addition

untie; unravel; undo (a fastening); unwrap / dispel (doubts); clear up (a matter)

solve (a problem); answer (a question); unravel (a riddle) / comb; untangle (hair)

teach; to instruct; give a lesson

instruction; teaching; school; lesson, class

mathematics (field of study)

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

(algebra) additivity

in class

a visit by a student's guardians to observe the class