1.08 g/cm^3
(when multiplying or dividing you use the least amount of significant figures to answer your question by which is the 19.5. That gives you 3 significant figures.)
4.83 km
(when adding or subtracting however you use the least precise the 4.810 goes into the thousandths place which is more precise then the 0.08 which only goes to the hundredths place.)