`86 - (2x + 1) : 3 = 69`
`=> (2x+1):3 = 17`
`=> 2x + 1 = 51`
`-> 2x = 50`
`=> x = 25`
=>(2x+1):3=17
=>2x+1=51
=>2x=50
hay x=25
53) 86 - ( 2 . x + 1 ) : 3 = 69
( 2 . x + 1 ) : 3 = 86 - 69
( 2 . x + 1 ) : 3 = 17
( 2 . x + 1 ) = 17 x 3
2 . x + 1 = 51
2 . x = 51 - 1
2 . x = 50
x = 50 : 2
x = 25