Suppose $x$ Is a Uniform Random Variable With $c = 20$ And $d = 90$

Multiple Choice

Suppose $x$ is a uniform random variable with $c = 20$ and $d = 90$ . Find the standard deviation of $x$ .

A) $\sigma = 31.75$
B) $\sigma = 2.42$
C) $\sigma = 3.03$
D) $\sigma = 20.21$