Salut! :)
1 + { 2 × [ 3 + ( a - 4 ) × 5 ] : 6 } × 7 = 8
{ 2 × [ 3 + ( a - 4 ) × 5 ] : 6 } × 7 = 8 - 1
{ 2 × [ 3 + ( a - 4 ) × 5 ] : 6 } × 7 = 7
2 × [ 3 + ( a - 4 ) × 5 ] : 6 = 7 : 7
2 × [ 3 + ( a - 4 ) × 5 ] : 6 = 1
2 × [ 3 + ( a - 4 ) × 5 ] = 1 × 6
2 × [ 3 + ( a - 4 ) × 5 ] = 6
3 + ( a - 4 ) × 5 = 6 : 2
3 + ( a - 4 ) × 5 = 3
( a - 4 ) × 5 = 3 - 3
( a - 4 ) × 5 = 0
a - 4 = 0 : 5
a - 4 = 0
a = 0 + 4
a = 4
