Centre of gravity

This task is about the centre of gravity.
The centre of gravity is the point in an object about which its weight is evenly balanced. Show how this concept might relate to the following situations.
a)
The placing of 18 empty and 6 filled water containers on a small truck. Shade the filled containers to show where you would place them so the load was most stable.
 

 
b) The design of a plastic duck for use in a bath so that it doesn't tip over easily. Draw your design, labelling the feature(s) that keep it from tipping.