A farmer has 72 \(kg\) of rice and 120 \(kg\) of wheat. Each bag must contain grain of only one kind. All bags must have the same whole-number weight, and the number of bags should be as small as possible.
 
Based on the above information answer the following questions:
 
(i) Write the prime factorisation of 72.
(ii) Write the prime factorisation of 120.
(iii) What weight should each bag hold?
 
(iv) How many bags are needed in all?