An object will keep sinking until it displaces a volume of water with an equal mass. In this case, I think it's easiest to assume a volume/mass of the brick, then figure out the mass of the styrofoam. So, let's assume a volume of 1 m^3 for the brick, this will give the brick a mass of 1400 kg. Therefore, we need to displace a volume of water with a mass of 1400 kg. Knowing that water has a density of 1g/cm^3 (or 1000kg/m^3) tells us that we need to displace 1.4 m^3 of water with HALF of the styrofoam block. So the total volume of the styrofoam must be 2.8 m^3. Now, take the ratio of the styrofoam volume to the brick volume. 2.8m^3/1m^3 = 2.8--answer choice c.