The question is not complete since it does not provide the complete information, here is the complete question:
Replace the infinitive in the sentence with the gerund form of the same verb.
The laughing boy in the boat likes to sail.
Verb in the grammatical structures can be used as infinitives (to + verb) or as gerunds ( verb + -ing) the infinitive that this sentence is using is "to sail" so that changing the form from infinitive to gerund would give us the form "sailing", in this case, the meaning is not affected by the change in the structure and remains the same.
The infinitive that is used in the given sentence above is "to sail". So to make this into a gerund form, it will become "sailing". Therefore, the new sentence will be like this: The laughing boy in the boat likes SAILING. Hope this answers your question.
