Aglacier advances toward the sea 0.004 mile anually. in 2010 the front of the glacier is 6.9 miles from the mouth of the sea. how far will it be from the sea in 2030.
by the way if it , were learning how to identify hidden problems in multiple-step problems.. so its a multiple step problem, i really don't understand this so some will really be appreciated.

You know where the glacier is now, and how far it moves in
one year.  The question is asking how close to the sea it will be
after many years.

Step-1 ... you have to find out how many years

Step-2 ... you have to figure out how far it moves in that many years

Step-3 ... you have to figure out where it is after it moves that far

The first time I worked this problem, I left out  the most important
step ... READ the problem carefully and make SURE you know
the real question.  The first time I worked the problem, I thought
I was done after Step-2. 



Step-1:  How many years is it from 2010 to 2030 ?

               (2030  -  2010)  =  20 years .

Step-2:  How far will the glacier move in 20 years ? 

               It moves 0.004 mile in 1 year.

              In 20 years, it moves 0.004 mile 20 times

              0.004 x 20  =  0.08 mile

Step-3: How far will it be from the sea after all those years ?

              In 2010, when we started watching it, it was 6.9 miles
              from the sea.

              The glacier moves toward the sea.
               In 20 years, it will be  0.08 mile closer to the sea.
               How close will it be ?

               6.9 miles  -  0.08 mile  =  6.82 miles  (if it doesn't melt)