PLEASE PLEASE help, none of my classmates and friends can figure this out we are suffering T_T

There are two parts to this solution:  The down part for the helmet, and the up part for the sound.  The down part has to be solved first, before the up part.

-- The helmet falls 78.4 meters.  How long does that take ?

In gravity,

Distance = (1/2) (acceleration) (Time²)

78.4 m = (1/2) (9.8 m/s²) (Time²)

Time² = (78.4 m) / (4.9 m/s²)

Time² = 16 sec²

Time = 4 seconds.

-- The crew heard the sound of helmet hitting the ground 4.23 seconds after their buddy dropped it.

We just calculated that it took 4 seconds for it to hit the ground.

So it took 0.23 second for the sound of the clunk to propagate the 78.4 meters back up to them.  What's that speed ?

Speed = (distance) / (time)

Speed = (78.4 m) / (0.23 sec)

Speed = 340.9 m/s

sleep paralysis is a parasomnia, events associated with sleep.

sleep paralysis happens when you are in the middle of waking up or falling asleep. it is the feeling of being conscious but unable to move. it definitely involves hallucinations.

i had a friend that had sleep paralysis and he told me a story one time where he was laying in bed and he couldn't move his body no matter how hard he tried and there was someone standing in the corner of his room coming towards him. he couldn't move and you can't "wake up" because you are already conscious. sometimes sleep paralysis can be triggered by frequent waking up during the night based off of multiple trips to the bathroom, or if you had ever been abused, sleep paralysis can start happening from things like that.

nah.   i'm just sleepy.