Răspuns :
321 : a x 9 - 3 = 960
321 : a x 9 = 960 + 3
321: a x 9 = 963
321 : a = 963 : 9
321 : a = 107
321 : 107 = a
3 = a
a = 3
321 : a x 9 = 960 + 3
321: a x 9 = 963
321 : a = 963 : 9
321 : a = 107
321 : 107 = a
3 = a
a = 3