Answer:
3/4 inch per year
Explanation:
A unit rate is the change in some quantity per one of another quantity. One common unit rate is miles per hour, which measure the number of miles traveled in one hour. Here, we're asked for the unit rate of plant growth per year, and we're told that at 16 years old, the plant measures 12 inches. Assuming this growth is linear (that is, it grows by the same amount each year), we can divide each quantity by the number of years (16) to find a unit rate of 12/16 = 3/4 inch per year.