We have the division:
It seems like a total quantity (3/4) is divided by a part (1/3).
It is not A, because 3/4 is the width (the part) and 1/3 is the area (the total), so it is not this case.
It is not B, because the area should be a multiplication of width and length.
It is not C, because the width should be calculated (1/3) / (3/4).
It is D, because the area is 3/4 and is divided by the length 1/3 to calculate the width.