1. Tell me the reason why you came late.
2. Tell me why you came late.
(In #1, 'why' is a relative adverb. In #2, 'why' is a relative adverb or an interrogative adverb. Is that right?)
3. This is how he solved the problem.
(In this sentence, 'how' is a relative adverb. 'the way' is deleted before 'how.' Is that right?)
Both "why" and "how" are interrogative adverbs.
#1 is awkward and wordy (delete "the reason" or delete "why"; #2 and #3 are fine. And yes, "the way" should not occur before "how."
1. In sentence #1, "Tell me the reason why you came late," the word 'why' is a relative adverb. It introduces a subordinate clause that functions as an adverbial clause modifying the noun 'reason.' To find the reason for coming late, you would need to look at the explanation provided by the person who came late.
2. In sentence #2, "Tell me why you came late," the word 'why' can function as both a relative adverb and an interrogative adverb. As a relative adverb, 'why' would introduce an adverbial clause modifying a noun, similar to how it functions in sentence #1. However, in sentence #2, 'why' is more commonly understood as an interrogative adverb, as it introduces a direct question about the reason someone came late. In this case, to find the reason for coming late, you would need to directly ask the person in question.
3. In the sentence, "This is how he solved the problem," the word 'how' is not a relative adverb. Instead, 'how' functions as an adverb of manner, explaining the manner or method in which he solved the problem. It does not have a deleted noun like "the way" preceding it.