What is the mass of an object if the density is 7.85g/l and the volume is 41.25ml

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)