Finding Density of a Floating Block

[superjen]

A uniform block of height 0.260 m, floats in water of density 1000 kg/m3. The bottom of the block is 0.2530 m below the surface of the water. What is the density of the block?

fb = mg
m=(pf)(v)
d = m/v

What i did was find the mass, using the volume of what is submerged, then when i found d using equation 3, i used the v of the whole block.
I know I am mixing something up here, but I am not sure what it is..

 

[mgb_phys]

The total weight of the block must equal the weight of water displaced.
If the block was the same density as water all of it would be under the surface, if it was half the density of water half of it would be below the surface.
What proportion is below the surface?