`a)`\(\dfrac{3x-18}{3}=21\)
\(\Rightarrow\dfrac{3\left(x-6\right)}{3}=21\)
\(\Rightarrow x-6=21\)
\(\Rightarrow x=21+6\)
\(\Rightarrow x=27\)
`b)7x+5x=156`
`=>12x=156`
`=>x=156/12`
`=>x=13`
\(\dfrac{\left(3x-18\right)}{3}=21\)
\(\left(3x-18\right)=21\times3\)
\(\left(3x-18\right)=63\)
\(3x-18=83\)
`3x = 63 + 18`
`3x= 81`
`x = 81 : 3`
`x = 27`
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`7x + 5x = 156`
`x . ( 7 + 5) = 156`
`x . 12 = 156`
`x = 156 : 12`
`x = 13`
\(\dfrac{\left(3x-18\right)}{3}=21\)
`3x - 18 = 21 xx 3`
`3x - 18 = 63`
`3x = 63 + 18`
`3x= 81`
`x = 81 : 3`
`x = 27`
`7x + 5x = 156`
`(7+5).1 = 156`
`12 .x = 156`
`x = 156 : 12`
`x = 13`
`(3x - 18)/3 = 21`
`=> 3x - 18 = 21 xx 3`
`=> 3x - 18 = 63`
`=> 3x = 63 + 18`
`=> 3x = 81`
`=> x = 81 : 3`
`=> x = 27`
__________________________________
`7x + 5x = 156`
`=> (7 + 5)x = 156`
`=> 12x = 156`
`=> x = 156 : 12`
`=> x = 13`
