Answer: 3.6 feet per year
Pick any column and divide the feet over the years
eg: 7.2/2 = 3.6 (column 1)
You can think of it as the ratio
7.2 feet: 2 years
and then divide both sides by 2 to get "1 year" on the right side
7.2 feet: 2 years
7.2/2 feet: 2/2 years
3.6 feet: 1 year
