a) Equal to 3/5 are: 6/10, 9/15, 12/20, 15/25, 18/30

b) Equal to 5/8 are: 10/16, 15/24, 20/32, 25/40, 30/48

c) Equal to 36/108 is: 13/54,1/3, 2/6, 3/9, 4/12 

The kilograms of rice left after the 2nd day sold is:

30 + 1/3 = 91/3(kg)

The kilograms of rice the store have at first is:

91/3 + 2/3 = 31(kg)

Answer: 31 kg