Joe is hiking a trail that is 30 miles long. after several days, he is two times as far from the beginning of the trail as he is from the end. how much further does he have to hike?

In order to answer this question let's suppose,
Joe is x miles from the beginning and y miles from the end. These assumptions are necessary to answer further:

Now,
x=2y
x+y=30
plugging in x=2y in the above equation
2y+y=30
3y=30
y=10

Hence, according to our calculations, Joe has to hike 10 miles further