Well we can already eliminate C and D because it says below sea level. If it is below sea level then we know the integer is a negative number since sea level is considered 0 and below 0 are negative numbers. The volcano is 33,000 feet and 17,976 feet is above ground. So to find out how much of the volcano is under sea level, we just subtract 33,000 - 17,976 ft which then we get 15,024 ft. But we are not done yet, since the number we got is the amount of feet the volcano is below sea level, we need to put a negative sign which then we get choice b. I hope this helps!