12 + { 2 × [ 32 + ( a - 24 ) × 5 ] : 4 } × 3 = 75
{ 2 × [ 32 + ( a - 24 ) × 5 ] : 4 } × 3 = 75 - 12
{ 2 × [ 32 + ( a - 24 ) × 5 ] : 4 } × 3 = 63
2 × [ 32 + ( a - 24 ) × 5 ] : 4 = 63 : 3
2 × [ 32 + ( a - 24 ) × 5 ] : 4 = 21
2 × [ 32 + ( a - 24 ) × 5 ] = 21 × 4
2 × [ 32 + ( a - 24 ) × 5 ] = 84
32 + ( a - 24 ) × 5 = 84 : 2
32 + ( a - 24 ) × 5 = 42
( a - 24 ) × 5 = 42 - 32
( a - 24 ) × 5 = 10
a - 24 = 10 : 5
a - 24 = 2
a = 2 + 24
a = 26 → numarul, aflat prin metoda mersului invers
