It's C. In order to be in standard form you have to have all your exponents in descending order. They don't all have to be there in order, the ones that are just have to go from highest to lowest.
We find the area of the total square which is 8in • 8in=64in^2 . Now we find the area of the small quadrilateral which is 4in•4in=16 in^2.
Now we subtract the area of the small quadrilateral from the big quadrilateral’s area 64in^2 -16in^2 leaving us with the are of 48in^2 of the figure
-x on both sides to get
x=15