Given, h=12.
b1=x+1.
b2=x+3.
The area of the trapezoid is,
[tex]\begin{gathered} A=\frac{1}{2}h(b_1+b_2) \\ =\frac{1}{2}\times12(x+1)(x+3) \\ =6(x+1)(x+3) \\ =6(x^2+3x+x+3) \\ =6(x^2+4x+3) \\ =6x^2+6\times4x+6\times3 \\ =6x^2+24x+18 \end{gathered}[/tex]Therefore, the area of the trapezoid is,
[tex]6x^2+24x+18[/tex]Hence, option C is correct.