I think you forgot to include that T is the midpoint of SV, but what this would mean is that ST = TV.
5x + 2 = 3x + 12
Subtract 2 from both sides.
5x = 3x + 10
Subtract 3x from both sides.
2x = 10
Divide both sides by 2.
x = 5
Now plug that x into ST.
ST = 5(5) + 2
ST = 25 + 2
ST = 27
