Answer:
[tex]9x^2+12x[/tex]
Step-by-step explanation:
Height of the Rectangle =3
Width of the Rectangle =[tex]3x^2+4x[/tex]
Area of a Rectangle = Height X Width
[tex]=3(3x^2+4x)\\=9x^2+12x[/tex]
The area of the rectangle is therefore given by:
[tex]9x^2+12x[/tex]