Answer:
I will call (as soon as he comes in).
Explanation:
An adverb clause is a group of related words that have at least a subject and a verb, and whose function is to act as an adverb, that is to say, to modify or add detail to adjectives, verbs or other adverbs. This type of clauses often answers questions such as "Why?", "How?", "When?", "Where?" and "In what circumstances?", and they often are introduced by subordinating conjunctions (as soon as, after, before, since) that link the adverb clause to another clause.
In the provided sentence, the adverb clause is "as soon as he comes in" as it modifies the main action (the verb) "will call", and answers the question "When will you call?". Furthermore, it is introduced by the subordinating conjunction "as soon as" that links the adverb clause to the clause "I will call."
