Since the coastal geologist estimates that the country’s beaches are eroding at a rate of 1.5 feet every year, they will erode by 1.5x feet in x years. Thus, if the beaches erode by 21 feet in x years, the equation 1.5x=21 must hold. The value of x is then
21
1.5
=14.Therefore,according to the geologist’s estimate, it will take 14 years for the country’s beaches to erode by 21 feet