70 - [ 4 × ( 5 + c × 7 ) - 2 ] : 3 = 8
[ 4 × ( 5 + c × 7 ) - 2 ] : 3 = 70 - 8
[ 4 × ( 5 + c × 7 ) - 2 ] : 3 = 62
4 × ( 5 + c × 7 ) - 2 = 62 × 3
4 × ( 5 + c × 7 ) - 2 = 186
4 × ( 5 + c × 7 ) = 186 + 2
5 + c × 7 = 188 : 4
5 + c × 7 = 47
c × 7 = 47 - 5
c × 7 = 42
c = 42 : 7
c = 6 → numarul, aflat prin metoda mersului invers