Pound is a unit of mass which is used in imperial, United States Customary and also used to measure the other uses of different system of measurement.
Kilogram is the base of unit of the mass in the metric system which also consist in the International System of Units. The SI unit of it is Kg. The main purpose of this is used to measure in engineering, science, commerce and it is called kilo in worldwide. It is also similar to the mass of one liter of water. It was firstly been defined in 1795 as a mass of a liter of water. It can be defined as by use three terms of fundamental physical constants as it take into consideration the speed of light, Planck Constant and specific atomic transition.  The word kilogram is derived from French word Kilogramme which also signify that it as a small weight. 
The solution of the problem is shown below:

As the bag contains 3.18 pounds
Each One Pound = 2.2kg
So, 3.18 pounds = 3.18/2.2 = 1.44 kg.