The rate at which customers are served at an airport check-in counter is a Poisson process with a rate of 8.1 per hour. The probability that more than 50 customers are served at the counter in the next 5 hours is P(Xp>50). If this is solved as a Poisson variable, the calculations will be tedious. So we use the normal approximation. Now, P(Xp > 50)=P(Z > a), where Z is the standard normal variable. What is the value of a? Please report your answer in 3 decimal places.