[ 15 - 4 × ( 3 x - 8 ) ] × 2 - 7 = 3
[ 15 - 4 × ( 3 x - 8 ) ] × 2 = 3 + 7
[ 15 - 4 × ( 3 x - 8 ) ] × 2 = 10
15 - 4 × ( 3 x - 8 ) ] = 10 : 2
15 - 4 × ( 3 x - 8 ) ] = 5
4 × ( 3 x - 8 ) = 15 - 5
4 × ( 3 x - 8 ) = 10
3 x - 8 = 10 : 4
3 x - 8 = 2, 5
3 x = 2, 5 + 8
3 x = 10, 5
x = 10, 5 : 3
x = 3, 5