Explanation:

- Start with the original family of 4 members: Their average weight is 45 kg.

- Total weight of these 4 members is: 4 * 45 = 180 kg.

- Grandparents arrive, making the family size 6 with a new average weight of 48 kg.

- Total weight of the 6 members is: 6 * 48 = 288 kg.

- To find the grandparents' combined weight, subtract the weight of the original family from the total weight: 288 kg - 180 kg = 108 kg.

- The average weight of the grandparents is 108 kg / 2 = 54 kg.

- Thus, the correct option is Option 4.

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