Mr.Riley was 30 feet above the water, which means he is at +30 above sea level. If he descends 100 feet, that means he goes 100 feet lower then that. 30 - 100 is equal to -70. He is 70 feet under water after he dived. You do not need to know the answer, but it helps to visualize the problem you have, therefore, finding the answer
he population 2016, this is more precise, will be 145116 people. If you just rounded the value of X to population growth rate to 1.176, then the population Uh in 2016 is 145,003 59.