HI! I just read some discussions about this but I still don't get it straight; when we use inches, meters, feet, as adjective, we write the number and the word( inch, meter) in singular right? I mean: 3-inch heel 20-dollar bill But i've seen that when using foot things become a little more complicated Which of the following is the correct one? a 5-feet-long rope a 5-foot-long rope Some people say that both are correct, but I'm sure that only one of them is so. Actually I've heard people saying: I'm 5 feet tall and also I'm 5 foot tall so ? What is the correct structure? Thank you!