Answer:
The sentence would be as follows: After Robert Fulton invented the steamboat, he tried it out on the Hudson River.
Step-by-step explanation:
Adverb clauses, also called adverbial clauses, are dependent clauses that function as adverbs. As they are dependent clauses, they must have a subordinating conjunction to connect them to the rest of the sentence.
A dependent clause is a group of words that can't stand on its own as a sentence because it does not represent a complete thought (2). They depend on the main clause to complete their meaning (3). In this case, the dependent clause (2) has been introduced by the subordinating conjunction after, adding information as regards the time in which the event took place.
1) After Robert Fulton invented the steamboat, he tried it out on the Hudson River.
2) * After Robert Fulton invented the steamboat
3) He tried it out on the Hudson River