How do you determine the scale number on the refractive index? What makes this 1.4606? How did they get that 6 at the end? Like how are the last two numbers determined if the 06 weren’t there if it was just 1.46?

Asample of hydrated tin (ii) chloride (sncl2) has a mass of 4.90 g. when it is dehydrated, it has a mass of 4.10 g. which is the correct chemical formula for the hydrate? sncl2•2h2o          sncl2•4h2o          sncl2•6h2o