Hello!
Let's start from the very beginning. He starts at sea level. This would make his elevation 0 feet.
Then, he dives 18 feet downwards. This would decrease his elevation by 18 feet, making it 18 feet below sea level.
Finally, he dives 24 feet downwards. This would decrease his elevation by another 24 feet. 24 feet below 18 feet below sea level would be 42 feet below sea level, as -18 - 24 = -42.
Therefore, your final answer is 42 feet below sea level.
Hope this helps!
