1) Â 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 Â
X = 5 × O,67/ 1 = 3,35 ,  a staghorn coral can grow 3,35 foot in 5 years Â