The total kg of rice bought is 75kg
Each week, 4.5kg is used,
Let the number of weeks be represented by n
The remaining amount of rice is represented by r
The relationship between the values above can be given as,
For 6 weeks, the kilogram of rice left where n = 6 is,
For 12 weeks, the kilogram of rice left where n = 12 is,
For w weeks, the kilogram of rice left where n = w is,
Hence, after 6 weeks, the remaining rice left is 48kg
Hence, after 12 weeks, the remaining rice left is 21kg
Hence, after w weeks, the remaining rice left is (75-4.5w)kg