What is the length of sr ?

9 units
12 units
15 units
18 units

 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.