The area of D is given by:

The average value of f over D is given by:
It rotates 180 degrees because its like 90 +90+180
180+90=270
Answer:
D: 12
Step-by-step explanation:
The entire segment KI is composed of the segments KJ and JI. So:

We know that KI is 15.
KJ is (2x-15) and JI is (2x-6). Substitute:

Solve for x. Combine like terms:

Add 21 to both sides:

Hence, the value of x is:

We know that JI is 2x-6.
We will substitute 9 for x to find JI. So:

Hence, our answer is D.