Assume the length x in minutes for a phone conversation is a random variable with probability density function: f(x) = ce^(-x/6) x> 0 and f(x) = 0 elsewherea / determine the value of cb/ determine the probability that the phone conversation last more than 18 minutesc/ determine the expected length of a phone conversationd/ find the variance and standard deviation of xe/ determine the probability that the phone conversaion will last within 2 standard deviations of the meanf/ find e[(x + 5)^2]