Explicație pas cu pas:
12 + { 12 + [ 12 - ( 12: a +5) : 3] :5} : 7 = 14
{ 12 + [ 12 - ( 12: a +5) : 3] :5} : 7 = 14 - 12
{ 12 + [ 12 - ( 12: a +5) : 3] :5} : 7 = 2
12 + [ 12 - ( 12: a +5) : 3] :5 = 2 × 7
12 + [ 12 - ( 12: a +5) : 3] :5 = 14
[ 12 - ( 12: a +5) : 3] :5 = 14 - 12
[ 12 - ( 12: a +5) : 3] :5 = 2
12 - ( 12: a +5) : 3 = 2 × 5
12 - ( 12: a +5) : 3 = 10
( 12: a +5) : 3 = 12 - 10
( 12: a +5) : 3 = 2
12:a + 5 = 2× 3
12:a + 5 = 6
12:a = 6-5
12 : a = 1
a = 12 : 1
a = 12