Probability of event occuring within an area


My problem is the following:
Within an area om about 30000 square kilometers there are 100 individals.
Each individual can be within an area of 1 square kilometer.
During 1 hour once a month there is a dangerous event that effects an area of 5 square kilometers.
The event can occur at one of three fixed possible locations.

What is the probability of an indivividual beeing within affected by a dangerous event?

And how would the calculation(formula) look like?

My own calculation is P(A) where P = 100 individuals X 5 km2 and A = 30000 km2.
Or am I missing som logic/variabels?