b1 = [5; 115; 12; 110; -96];
    
b2 = [5; 115; 11; 110; -96];
    
    
A = [ -1 2 3 -4 1
      69 -98 -7 86 -19
      10 -12 -2 11 -3
      70 -100 -10 90 -20
      -56 78 4 -67 15];