Răspuns :
9 + 8 × [7 + 6×(5 + 4×a)] = 881
8 × [7 + 6×(5 + 4×a)] = 881 - 9
8 × [7 + 6×(5 + 4×a)] = 872
7 + 6×(5 + 4×a) = 872 : 8
7 + 6×(5 + 4×a) = 109
6×(5 + 4×a) = 109 - 7
6×(5 + 4×a) = 102
5 + 4×a = 102 : 6
5 + 4×a = 17
4×a = 17 - 5
4×a = 12
a = 12 : 4
a = 3
8 × [7 + 6×(5 + 4×a)] = 881 - 9
8 × [7 + 6×(5 + 4×a)] = 872
7 + 6×(5 + 4×a) = 872 : 8
7 + 6×(5 + 4×a) = 109
6×(5 + 4×a) = 109 - 7
6×(5 + 4×a) = 102
5 + 4×a = 102 : 6
5 + 4×a = 17
4×a = 17 - 5
4×a = 12
a = 12 : 4
a = 3