If variance of a random variable X is "K"..
Now for a random variable aX+b the variance is (a)^2 times K.
variance of the random variable X is 9 thenstandard deviation of the random variable -4x+8 .
now Comparing this with ax+b a=-4
new variance is 16x9=144.
But standard deviation is square root of variance.
So,square root of 144 is 12.
so answer is C-12