A rectangle is just a geometric shape; it doesn't have a "density".A material shaped like a rectangle can have a density; in this case, the density will depend on what material you are using.
u will need the density. density = mass / volume so mass = volume x density
The area of rectangle is : 56.0
In a simple way, since density = mass /volume, the density of an object can be changed by changing either mass or volume of an object .
Density. An object will float in a substance if its density is less than the density of the substance. The density of water is 1 kg /L or 1 g/ cm3. Anything with a density less than this will float.
It's actually pretty easy. If the density of the substance is higher than the density of water, the object will sink. If the density of the substance is lower than the density of water, the object will float. Be aware though that various substances may have dissolved into the water, thus changing its density. For example, seawater has a different density than fresh water.