Final answer:
The correct conversion factor from km to ft is 3,280.84, and after multiplying 12 km by this factor, Joe traveled 39,370.08 feet.
Step-by-step explanation:
The conversion factor from kilometers to feet is known to be 1 km = 3,280.84 feet. To convert kilometers to feet, you multiply the number of kilometers by this conversion factor. Therefore, to find out how many feet Joe traveled when he traveled 12 kilometers, we perform the following calculation:
12 km * 3,280.84 ft/km = 39,370.08 ft
Based on the given options for Joe's travel distance in feet, the closest answer is (a) 39,370.08 feet.