Răspuns :
1 128 - b + 54 = 813
1 128 - b = 813 - 54
1 128 - b = 759
b = 1 128 - 759
b = 369
1 128 - b = 813 - 54
1 128 - b = 759
b = 1 128 - 759
b = 369
1128-b+54=813
1128-b=813-54
1128-b=759
b=1128-759
b=369
Verificare:1128-369+54=813
1128-b=813-54
1128-b=759
b=1128-759
b=369
Verificare:1128-369+54=813