First he is not locking properly up
That would be to find the age of the fossil. Its called radiometric dating.
The density is the ratio between mass and volume. So the mass is the product between density and volume. But! You have to control the units of measure.
7.85 g/l = 0.00785 kg/l
41.25 ml = 0.04125 l
Mass = (0.00785) x (0.04125) = 0,00032381 kg ---> 0,32381 g
(I hope this is right )
