15.7 (USCS units) A pile of iron powder weighs 2 lb. The particles are spherical in shape and all have the same diameter of 0.004 in. (a) Determine the total surface area of all the particles in the pile. (b) If the packing factor = 0.6, determine the volume taken by the pile. Note: the density of iron = 0.284 lb/in³. (a) in³ x 10³ in², (b)