Question 256585
Your problem is garbled. We are not clairvoyants here. 
Why did you try to show 25=2x+3?
I don't understand the first part.
find the value of the variable andST if S is between R and T; RS=2x,ST=3x,RT=25 
What variable? 
What is ST?
What is R? T?
You have to tell us what you are talking about. Is there a figure(drawing)?