poisson question

OK here is an exercise that i don't understand how to solve: imagine a balcony that attends client.
For every 10 min. the number of people getting attended follows a Poisson distribution with an expected value of 2. the balcony only works from 9am till 12 am, and only attends 40 people at Max.

now the question is: what is the probability of not attending all clients in one morning (9am till 12am)?

ps: ok so from wat i got is the expected value of180 min (9am till 12am) is 36 ...
you are trying to find the probability that there were more than 40 people at the balcony between that time. P(X>40)
In poisson distribution expected value E(x)=lambda=2
So you need to find the probability that there were 40 people or less on the balcony P(X<=40) and then subtract that number from 1 to get P(X>40)
You should be able to find the equation to use in your book under Poisson Distribution.

p.s. after you do it by hand you can check your answer by googling Poisson Distribution Calculator online and plug in you lambda and x and compare