A rectangular air mattress is 200 cm long, 50 cm wide and 8 cm thick. If it has a mass of M=2 kg, what additional mass X can it support in water? Hint: Volume=L x W x H; Archimedes Forces B= (density of water) x V x g; M+X=B
so, what volume of water does it displace if submerged??
How much mass is that?