Answer
$3x^2+8x$
Work Step by Step
Let A be the area of the larger rectangle. Hence, A = 2x(2x+6)=$4x^2+12x$
Let B be the area of the smaller rectangle. Hence, B = x(x+4) = $x^2+4x$
Subtract B from A.
ans = A - B = $4x^2+12x$ - $x^2-4x$ = $3x^2+8x$
