23 - [ 26 - ( 5 × b - 9 ) ] : 5 = 24
[ 26 - ( 5 × b - 9 ) ] : 5 = 23 - 24
[ 26 - ( 5 × b - 9 ) ] : 5 = - 1
26 - ( 5 × b - 9 ) = ( - 1 ) × 5
26 - ( 5 × b - 9 ) = - 5
5 × b - 9 = 26 - ( - 5 )
5 × b - 9 = 31
5 × b = 31 + 9
5 × b = 40
b = 40 : 5
b = 8
