Answer
The correct answer is (d) 9.
Work Step by Step
We can find the kinetic energy of a person who is walking.
$K_1 = \frac{1}{2}mv^2$
The speed of the person on a bike is $3v$. We can find the kinetic energy of the person when they are biking.
$K_2 = \frac{1}{2}m(3v)^2$
$K_2 = 9\times \frac{1}{2}mv^2$
$K_2 = 9\times K_1$
The correct answer is (d) 9.
