Answer:
[tex]12x^2+4x[/tex]
Step-by-step explanation:
The area of a square or rectangle can be found by multiplying the width by the height. Since we now both, we can create an expression.
[tex](3x+1)*(4x)[/tex]
Now we can apply the distributive law/property to expand the expression.
[tex]3x(4x)+1(4x)[/tex]
Finally, we can simplify.
[tex]12x^2+4x[/tex]