Poisson Distribution Question
So I got a summer homework package from school (Doh), and I need to teach myself Poisson Distribution before school starts. So here's the question I've been stuck on for a while. (I need help on b.)
The number of faults in glass sheets occur at a rate of 2.1 per sq. metre. If a 1x1 sq. m glass sheet contains at least 3 faults it is returned to the manufacturer.
a) Find the probability that a 1x1 sq. m sheet is returned to the manufacturer.
b) Six such glass sheets are inspected. What is the probability that at least half of them are returned to the manufacturer? (Here's the answer provided: 0.6817)
It would be nice if you can show me the work and proper notation, because I barely have a clue.