Question

a hiker descends from a mountain peak. if the hiker descends at a rate of 700 ft every half hour, what is the hikers elevation relative to the peak after 3 hours

Answer 1

In 3 hours there is 6 half hours. 
So, in order to get the hikers elevation relative to the peak, multiply like this:
$700\times6=4200$

Answer 4200 feet

Answer 2

If the hiker covers 700 feet every 30 minutes. In an hours time the hiker is 1400 feet relative to the peak of the mountain. 30 minutes later which is actually 1 hrs 30 minutes later the hiker is 1400 + 700 = 2100 feet relative to the peak of the mountain. In another 30 minutes time (now 2 hours later) the hiker is 2100 + 700 = 2800 feet relative to the mountain peak. 30 minutes later (now 2hr 30 minutes) hiker is 2800 + 70. = 3500 feet and so in 3hrs time the hiker is 3500 + 700 = 4200 feet relative to the peak of the mountain.