The number of feet the shoreline is eroding per year is 1 ⅓ feet.
How many feet are eroding per year?
Rate of shoreline eroding per 3 months = 1/3 foot
Number of 3 months in a year = 12 months / 3 months
= 4
Number of feets of the shoreline eroding per year = Rate of shoreline eroding per 3 months × Number of 3 months in a year
= 1/3 × 4
= 4/3 feet per year
Therefore, the shoreline erodes 1⅓ feet per year