DS and x = {1, 2, 3, 4, 5, 6}. Let X be a discrete random variable with pmf fx(x0), where 0 = {1,2,3} fx (x0) = x/21, 0 1/6, I(x = 3), 03 = 1 2 = Find an maximum-likelihood estimator of 0. (Here for simplicity we only consider a single random variable instead of a random sample. Note: MLE is a function of X but it may not be expressed using a nice-looking formula.)