`a, => x/2 = x/3`
`=> 3x = 2x`
`=> x = 0`.
`b, => (4x+5):3 - 11 = 4`
`=> (4x + 5) : 3 = 15`
`=> 4x + 5 = 45`
`=> 4x = 40`
`=> x = 10`
`c, 4x = 84`
`=> x = 84/4 = 21`
`d, 0.(7-x) = 0`
`=> 7 - x in RR`
`=> x in RR`
`x : 2 = x : 3`
`x/2 = x/3`
`=> (3.2) . x/2 = (3.2) . x/3`
`6 . x/2 = 6 . x/3`
`=> 3x = 2x`
`=> 0`
_________________
`(4x +5):3 - 121 : 11 = 4`
`(4x +5):3 -11 = 4`
`(4x+5):3 = 4+11`
`(4x+5):3=15`
`(4x + 5) = 15 xx 3`
`(4x+5) = 45`
`4x = 45 - 5`
`4x = 40`
`x=40:4`
`x=10`
_____________________
`5x - x = 84`
`5x-1.x=84`
`(5-1)x=84`
`4x=84`
`x=84:2`
`x=21`
________________________
`0.(7-x)=0`
`=>` \(\left[{}\begin{matrix}x=0\\7-x=0\end{matrix}\right.=>\left[{}\begin{matrix}x=0\\x=7\end{matrix}\right.\)