Final answer:
The scuba diver will be 2.5 feet below the surface after 15 seconds.
Step-by-step explanation:
To determine the location of the scuba diver after 15 seconds, we need to calculate how many times the diver can swim 0.5 feet towards the surface in 15 seconds. Since the diver swims 0.5 feet every 3 seconds, we divide 15 seconds by 3 seconds to get 5. This means the diver can swim towards the surface 5 times in 15 seconds. Therefore, the location of the scuba diver, relative to the surface, after 15 seconds is 5 times 0.5 feet, which is 2.5 feet below the surface.