Step 1 :The variance of a Poisson distribution is equal to its mean, so the variance is \( \boxed{3.9} \).
Step 2 :The standard deviation is the square root of the variance, so the standard deviation is \( \boxed{2.0} \).
Step 3 :The mean number of strokes for an 18-hole round is 18 * 3.9 = 70.2.
Step 4 :The probability of having more than 72 strokes is the same as 1 minus the probability of having 72 or fewer strokes.
Step 5 :We can use the cumulative distribution function (CDF) of the Poisson distribution to find the probability of having a certain number of strokes or fewer.
Step 6 :The probability of the golfer having more than 72 strokes in an 18-hole round, rounded to the nearest thousandth, is \( \boxed{0.385} \).