Question

The underlying rock ledge of Canada's Horseshoe Falls is cut back about 2 feet each year by erosion. Calculate how much the rock ledge will erode over a 7-year period of time.

Answer 1

hint: after the first year, 2 feet are eroded
second year, 4 feet are eroded
third year, 6 feet are eroded, etc.

so the formula must be

feet loss due to erosion = 2 * the number of years

so, how many feet are lost after 7 years?

Answer 2

erosion = 2 * the number of years
number of years = 7

erosion = ?