Answer
$4x^2+5x+1$
Work Step by Step
The area $A$ is the sum between the area of a rectangle with dimensions $x$ and $3x+1$ and a right triangle with legs $2(x+1)$ and $3x+1-x$::
$A=\frac{1}{2}(3x+1-x)[2(x+1)]+2(x+1)x$
$A=(2x+1)(x+1)+2x^2+2x$
$A=2x^2+3x+1+2x^2+2x$
$A=4x^2+5x+1$
Thus, the expression for the area is:
$$4x^2+5x+1$$
