`(x+3)^3-x(3x+1)^2+(2x+1)(4x^2-2x+1)=28`
`<=>(x+3)(x^2+6x+9)-x(9x^2+6x+1)+8x^3+1=28`
`<=>x^3+9x^2+27x+27-9x^3-6x^2-x+8x^3+1=28`
`<=>3x^2+26x=0`
`<=>x(3x+26)=0`
`<=>`\(\left[ \begin{array}{l}x=0\\3x+26=0⇔x=\dfrac{-26}{3}\end{array} \right.\)
`=>x={0;(-26)/3}`