Explanation:

- The average weight of 6 girls increases by 2.5 kg. This means the total weight increases by $6\times 2.5=15$ kg.

- Originally, the total weight of the 6 girls includes the girl weighing 38 kg.

- When she is replaced by a new girl, the total weight increases by 15 kg.

- So, the weight of the new girl is $38+15=53$ kg.

- Option 1: 46 kg – This is not correct. It does not account for the 15 kg increase.

- Option 2: 58 kg – This is higher than needed.

- Option 3: 53 kg – This matches the required increased weight correctly.

- Option 4: 49 kg – This is not enough for the increase.