Răspuns:
a = 12
Explicație pas cu pas:
3+3x[3+3x(3+3x3)]=(3xa+3)X3+3
3+3x[3+3x(3+9)]=(3xa+3)X3+3
3+3x[3+3x12]=(3xa+3)X3+3
3+3x[3+36]=(3xa+3)X3+3
3+3x39=(3xa+3)X3+3
3+117=(3xa+3)X3+3
120=(3xa+3)X3+3
(3xa+3)X3= 120 -3
(3xa+3)X3= 117
3xa + 3 = 117 : 3
3 x a + 3 = 39
3 x a = 39 - 3
3 x a = 36
a = 36 : 3
a = 12