To solve this problem it is fundamentally, just look for the volume of the gas and convert it to cm3. At STP 1 mole = 22.4 liters. 8.00 moles x 22.4 liters/mole = 179.2 liters = 179,200 cm^3 Then. get the cube root of 179,200 cm^3. This would be equal to 56.38 cm and thus would be the length of the edge of this cube.
Ca=40.07841 ,Nitrogen=14.006722 ,Oxygen15.99943
molar mass= (1xMW of Ca)+(2xMWof N)+(6x MW of oxygen)
Molar mass (molecular weight) of Ca(NO3)2 is 164.0884 g/mol