Answer: THe correct option is (C) 15.
Step-by-step explanation: We are given to find the length of SR in the right-angled triangle SRQ as shown in the figure.
Since RT is perpendicular to the hypotenuse SQ, so triangle RTQ and SRT are also right-angled triangles at angle RTQ and RTS respectively.
Also, RQ = 20 units and TQ = 16 units.
Using Pythagoras theorem in triangle RTQ, we have

Now, since RT is perpendicular to the hypotenuse of ΔRST, so we get

Again, using Pythagoras theorem in right-angled triangle RST, we get

Thus, the length of SR is 15 units.
Option (C) is CORRECT.