Hi There!
So the rock edge is cut back 2 feet each year by erosion and we have to figure out how much it will be cut back by 7 years using this knowledge so.
2 feet each year
2 + 2 + 2 + 2 + 2 + 2 + 2
or
7 x 2
=
14 so:
The Rock Ledge will have eroded 14 feet at the end of 7 years