Buoyancy of wood block problem help

[map7s]

A block of wood floats on water. A layer of oil is now poured on top of the water to a depth that more than covers the block. If 91% of the wood is submerged in water before the oil is added, find the fraction submerged when oil with a density of 883 kg/m3 covers the block. (Do not neglect the buoyant force of air before the oil is added.)

I would just like help on getting started on this problem. I looked at the equation Vsub=Vs(p,s/p,f) but I wasn't sure how/what values to substitute if they are given as percentages. I tried setting up the equation as 0.91=p,s/p,f but I wasn't sure what I would be solving for/plugging in if I had done that.

 

[QuantumCrash]

Perhaps drawing a free body diagram for analysing the block of wood should help. You should find that there are four forces acting. You can also find the weight of the wooden block from the initial situation.