the picture in the attached figure
we know that
area of the the shaded region=area of rectangle -area of a kite
area of rectangle=(3x+x)*(x+x)----> 4x*2x---> 8x²
area of a kite=(1/2)*[d1*d2]
where d1 and d2 are the diagonals
d1=4x
d2=2x
so
area of a kite=(1/2)*[4x*2x]----> 4x²
area of the the shaded region=8x²-4x²-----> 4x²
the answer is
4x²