1) first step
in this exercise you must establish a relation of proportion
if a staghorn coral can add as 0,67 foot per year then in 5 years can grow X
0,67 foot ______ 1 year
X__________ 5 years
X = 5 × O,67/ 1 = 3,35 , a staghorn coral can grow 3,35 foot in 5 years