A vessel contains oil (density =0.8 gm/cm3) over mercury (density =13.6 gm/cm3). A homogeneous sphere floats with half its volume immersed in mercury and the other half in oil. Find the density of the material of the sphere in gm/cm3.
a. 3.3
b. 6.4
c. 7.2
d. 12.8