Here are the answers based on your questions:
Question 1: One of the main causes of European exploration in the 15th and 16th centuries was the Search for new trade routes & luxury goods.
Question 2: Mercantilism impacted the American colonies by restricting the colonies' ability to trade with countries other than Britain.
Question 3: The impact of the discovery of the Americas on European exploration included All of the above (Increased competition between European powers, Expansion of the Atlantic slave trade, Introduction of new crops and animals to Europe).