Choice D is correct. Since density is mass per unit volume, the mass is the density times volume. The volume of a right rectangular prism is the product of the lengths of the sides. Therefore:
mass =(2.8 grams per cubic centimeter )×(30 centimeters ×40 centimeters ×50 centimeters ) mass =(2.8 grams per cubic centimeter )×(60,000 cubic centimeters ) mass =168,000 grams ​
Choice A is incorrect and may result from adding, instead of multiplying, the lengths of the sides to find the volume. Choice B is incorrect and may result from the same error as in choice A, as well as a place value error. Choice C is incorrect and may result from a place value error when finding the volume.