Since each ball is replaced after it is drawn, the probability of drawing a black ball on any given draw is 8 / (6 + 8) = 4 / 7. The probability of drawing 5 black balls in a row is the product of the probabilities of each individual draw, since the draws are independent of each other. Therefore, the probability of drawing 5 black balls in a row is:
(4/7) * (4/7) * (4/7) * (4/7) * (4/7) = 0.0724
Rounding to three decimal places, the probability that all 5 balls drawn from the urn are black is 0.072.