verbal arithmetic

difficult / hard, probably impossible

to be masked, to wear a mask

mask (cover for the face) / anonymous

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

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

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

Counting, calculation

(historical) mathematics

(historical) sangaku (ema on which is written an original maths (和算) problem and solution)