Can someone walk me through how to work this I have no clue where to start. I have converted grams to moles and Celsius to kelvin but I don't know where to go from there.

Thank you!

A piece of dry ice (solid CO2, d = 0.900 g/mL) weighing 21.0 g is placed in a 0.870 L bottle filled with air at 0.813 atm and 550.0°C. The bottle is capped, and the dry ice changes to gas. What is the final pressure inside the bottle?

21.0g= 0.477mol CO2
550C=823K

A couple of ways to look at this. The short way is

pCO2 = nRT/V = 0.477*0.08206*823/0.870 = ?
pair = 0.813
Total P = pair + pCO2 = ?

The long way is
nair = PV/RT = 0.08206*0.870/0.08206*823 = about 0.0105 mols air.
Total mols = 0.477+0.0105 = ?
Then p = n(total)RT/V.