Step 1: Let's recall that the midpoint of a line segment is the middle point and it is equidistant from both endpoints.
Step 2: Upon saying that, we have that:
ST = TU
Replacing with the values given in the exercise:
4x = 3x + 16
4x - 3x = 16
x = 16
Step 3: Now you can find the value of ST and TU easily:
ST = 4x
TU = 3x + 16