Strontium Oxide Has a Face Centered Cubic Unit Cell of Oxide

Strontium oxide has a face centered cubic unit cell of oxide ions with the strontium in octahedral holes.The radius of Sr²⁺ is 127 pm and the radius of O^2- is 135 pm.What is the density of strontium oxide? (100 cm = 1 $\times$ 10¹² pm)

A) 0.209 g/cm³
B) 1.20 g/cm³
C) 2.39 g/cm³
D) 3.59 g/cm³
E) 4.78 g/cm³