Answer:
2 
Step-by-step explanation:
Kim was walking down a rocky path. For 4 minutes, the elevation dropped steadily. All together it dropped 8 feet.
So, the change in elevation per minute for the 4 minutes is given by,

= 2 
(Answer)
Y=4x because 20/5 equals 4
I believe that the missing letter would be E and S which would be in between S and T
It is a 125% increase from 20 to 45
X=6+3y
Let me know if you need the steps:)