Physics problem!! A flat slab of styrofoam, with a density of 32 kg/m^3, floats on lake...?

there's different grade density can float between 48 and 55 lbs. of weight per cubic foot if u cant find that much you can add to it by layering on some insulating foam in a can that should give another 40+ mounds of lift but is stronger than then styrofoam it's like 1.50-$2 a can cheap can be found in any hard were store on must be layered bit by bit when i was younger me and my friend mad one from only the can foam/card board frame made a 6 foot boat like thing took 10 cans thats like $23 or so the good days lol.