7 + { 7 + 7 × [ 7 + 7 × ( a + 7 : 7 ) ] } = 455
7 + { 7 + 7 × [ 7 + 7 × ( a + 1 ) ] } = 455
7 + 7 × [ 7 + 7 × ( a + 1 ) ] = 455 - 7
7 + 7 × [ 7 + 7 × ( a + 1 ) ] = 448
7 × [ 7 + 7 × ( a + 1 ) ] = 448 - 7
7 × [ 7 + 7 × ( a + 1 ) ] = 441
7 + 7 × ( a + 1 ) = 441 : 7
7 + 7 × ( a + 1 ) = 63
7 × ( a + 1 ) = 63 - 7
7 × ( a + 1 ) = 56
a + 1 = 56 : 7
a + 1 = 8
a = 8 - 1
a = 7
