Which on of these numbers is not like the others? 25, 16, 49, 63, 81

Ihave trouble finding the nth term of a linear sequence

What is the 17th term in the arithmetic sequence in which a6 is 101 and a9 is 83

Amountain climber starts a climb at an elevation of 453 feet above sea level at his first rest stop he has climbed 162 feet and by his second rest stop he has climbed another 207 feet its getting late in the day so the climber starts his way down if the climber desends 285 feet how much does he need to ascend or descend to return to the original starting point