How much Load Air Mattress can carry?

Question

A beach mattress filled with air has a volume of 120 L and a mass of 6.0 kg.

1. What is the miximum load the mattress can carry on the surface of the Dead Sea? The saline water of the Dead Sea has a density of 1240 kg/m3 (m raise 3)

(Assume that the mattress retains its shape and volume regardless of load)

Answer 1

If a very heavy weight was placed on the mattress, all that would happen is that it would begin to submerge under the water.

Answer 2

Well, for a start, 1240 kg.m^3 = 1.24kg/L

120L * 1.24kg/L = 149kg

149 - 6.0(the mass of the mattress itself)  = 143kg