144 miles as you can see from the slope in the graph
The question is worded a bit strangely (in my opinion anyway), but I think your teacher wants you to describe how exponents work.
Let's say we had the expression 
The base is 5 as its the bottom most value (think of something like the base of a tree or building). The exponent is 3.
The exponent of 3 tells the reader to multiply the base 5 by itself 3 times like so

With larger exponents, it becomes more tedious to write out all the repeated multiplications, which is why many calculators have an exponent button to save time.
Four hundreds two tens and three ones
Y2-Y1
Over X2-X1 and then there is your slode
I think you do 120 divided by 5, but I could be wrong.