Answer:
Number 1 is complex, Number 2 is compound, Number 3 is simple.
Step-by-step explanation:
Number 1 is complex because it has both a dependent clause (After they finished studying) and an independent clause (they went to the store). The subordinating conjunction in this case is "after".
Number 2 is compound because it has two simple sentences (The voyage was difficult & it was worth it) joined by the conjunction "but".
Number 3 is a simple sentence with no conjunctions.