An element has ccp packing with a face-centered cubic unit cell. Its density is 1770 kg/m3 and the unit cell volume is 1.50 x 10-28 m3. Calculate the molar mass (g/mol) of the element to three significant figures.
The mass = volume x density
You know volume and density, solve for mass of unit cell.
Then mass of a unit cell = 4*atomic mass/6.022E23
Substitute mass into th equation and solve for atomic mass and round to 3 s.f. Post your work if you get stuck.