[tex]\qquad \qquad\huge \underline{\boxed{\sf Answer}}[/tex]
Let's solve ~
[tex] \qquad \sf \dashrightarrow \: (x {}^{3} - 4x {}^{2} + 1) + (3 {x}^{2} + x)[/tex]
[tex] \qquad \sf \dashrightarrow \: {x}^{3} - 4 {x}^{2} + 1 + 3 {x}^{2} + x[/tex]
[tex] \qquad \sf \dashrightarrow \: {x}^{3} - 4 {x}^{2} + 3x {}^{2} + x + 1[/tex]
[tex] \qquad \sf \dashrightarrow \: {x}^{3} - {x}^{2} + x + 1[/tex]
