B) 6.78x10 cubed turns into 6780 as a ordinary number. Diameter = radius x 2 therefore we divide 6780 by 2 giving us the radius which is *3390km*
C) We need to turn the standard for into ordinary number for the masses of Earth and Mercury and then minus the mass of Mercury from Earth from which we then get *5.64x10 to the power 24*.