The length of ST is equal to 8 units.
Data;
The segment of a line is basically a straight line from one point to another.
The line segment is SU and the mid-point is TU
solving this mathematically,
[tex]SU = TU + ST[/tex]
Substitute the values into the equation
[tex]su = tu + st\\18 = 10 + st\\st = 18 - 10\\st = 8[/tex]
From the calculation above, the length of ST is 8.
Learn more on segment of a line here;
https://brainly.com/question/3573606