The given expression is
[tex] (x+4)(3x^2 +2x) [/tex]
And in the second factor, x is common. So on taking x out, we will get
[tex] (x+4)(x)(3x+2) = x(x+4)(3x+2) [/tex]
We can expand it by distributing , that is
[tex] (x+4)(3x^2 +2x) = x(3x^2 +2x) +4 (3x^2 +2x) [/tex]
[tex] = 3x^3 +2x^2 + 12x^2 +8x [/tex]
Combining like terms,
[tex] = 3x^3 +14x^2 +8x [/tex]
And that's the expanded form ., and the given expression can also be written in that way .