SAT Mathematics Practice Test 2

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 $1.5\mathit{x}$ feet in x years. Thus, if the beaches erode by $21$ feet in x years, the equation $1.5\mathit{x}=21$ must hold. The value of $\mathit{x}$ is then $\frac{21}{1.5}=14$.Therefore,according to the geologist’s estimate, it will take 14 years for the country’s beaches to erode by 21 feet